This is a guide for new cubers who are considering buying a better cube. I will explain much of the terminology that you might see, and explain what things to look for in a speedcube.
Most speedcubers use a "DIY" (Do it yourself) cube. Some DIY cubes must be assembled, and some come already assembled. What they all have in common is that the center caps on each side can be removed to reveal screws. You can adjust these screws to change the tension of the cube. A regular storebought cube can not be adjusted in this way.
The first thing to consider, is do you need a DIY cube? Getting a DIY will NOT magically cut your times in half. It might shave a few seconds off of your times, but don't expect much. More importantly, is that DIY cubes can just feel much better in your hands. If you have a cube that doesn't always perform how you want it to, then you can get frustrated. Having a nice cube will make your cubing sessions more enjoyable (at least in my opinion). There are many different kinds of DIYs, and they are all slightly different. Most DIY cubes are given a letter designation, such as "Type A, or Type C", while some cubes have a name, such as the Cube4You cube.
There are a number of factors at work which make each DIY different:
The type of plastic used - Different types of plastic can feel different when you are moving the cube around. Some of it is very smooth or soft, while others might be made with harder plastic.
Tendency to pop - "Popping" means that a piece of your cube pops out while you are solving it. This is usually directly related to how tight the screws are. If you loosen your cube too much, pieces will pop more easily, and if you tighten it enough, pieces probably wont pop at all. This varies from cube to cube though, so some cubes may tend to pop even when they are very tight, while other cubes may not pop even if they are quite loose.
Tendency to lock up - Locking up is when you try to turn a side of the cube, and it does not turn. This is usually because the layers are not perfectly aligned, and the edges of the cubes hit each other, preventing the turn. Some cubes are more forgiving than others, and hardly ever lock up.
Ability to cut corners - Cutting corners means than you can turn a layer even when it is not fully aligned. This allows you to begin turning one layer before you have completed the previous turn, which means you can string together moves more quickly and easily.
Speed - How easily and quickly can you turn the sides? Like many other factors, this is also directly related to how tight you have the cube. Some cubes are fast and loose even at fairly tight settings.
Other factors - cubes all have a number of other factors at work which make them different from one another. The cubies may have a unique shape, the core and screws/springs may differ, and any number of other things.
It is important to realize that each person may be looking for different things in a speedcube. One persons favorite type of cube may be another persons least favorite. DIY cubes are generally cheap (usually cheaper than a storebought rubik's!), so you should probably do yourself a favor and buy a few different ones. Also, some cubes may become better over time, as they get "broken in", so don't let your first impression of a cube cloud your thoughts of it. Also, you will usually want to lubricate your cube, so it can turn more quickly and easily. Often, lubrication can make a HUGE difference in how a cube responds. DO NOT use petroleum jelly or WD-40 on your cubes. I recommend a lubricant called Jig-a-loo, which is sold at Wal-Mart and comes in an orange can.
I have purchased a few DIY's, but by no means have I tried them all. I have written up reviews of each one that I own, so you can get a general idea about them. Keep in mind that these are only my own personal opinions based on the cube that i received. In some cases, it could be that I simply received a cube that performs significantly better or worse than most cubes of that type. In general though, all cubes of the same type should be roughly the same. If you disagree with my opinions on a cube, please feel free to post your own viewpoint. Also, though I have assigned a numeric rating to each cube, this is still just my subjective opinion, and is basically just a rating of how much I like a cube. A higher rating just means that I am more likely to use than cube than one I have rated lower. The images I have posted of each cube are taken either from Cube4You.com or rubikfans on ebay. I purchased all of my cubes from these two stores.
If you want a wide variety of opinions, and a hands-on look at different kinds of cubes, try searching for each type of cube on youtube, and you should find numerous video reviews for each one!
This is the first cube that most people get. The tension on it can not be adjusted, it locks up a lot, but it absolutely does not pop. It's very hard and durable. It can get faster and better once it has been broken in a lot.
Rating: 5/10 (Just my opinion)
Type A (third model)
Ok first off, I need to explain a bit about the Type As. It seems there are a lot of different Type As. There is the Old Type A, which many people claim is the best one. Then there are Type A II and Type A III, which most people say are not good. And then there is Type A third model (not to be confused with type A III). Here are the differences between them all, as I understand it: The old type A is just a normal cube with no special features. Type A II added "tracks" onto the pieces. Type A III has the tracks, and added "tabs" onto the edge pieces. Type A third model has the tabs, but not the tracks.
The third model is the one that I own. This cube is pretty smooth and fast, cuts corners VERY well, and doesn't tend to pop or lockup. It came with some plastic tabs that go in the edge pieces which are supposed to prevent popping. I was unable to insert the tabs that go on the edge pieces, as they literally would not go in. It works just fine without these pieces though. It tends to be kinda loud in my opinion. The center caps stick out and the pieces just generally don't seem to line up properly. While it's an all-around good cube, it just doesn't "feel" right to me because of this. This cube required assembly.
Rating: 8/10 (Just my opinion)
I've heard that type C's were supposed to be great cubes, but mine doesn't feel too great. First of all, it just doesn't turn very smoothly. I've lubed it and everything, but the sides are grinding against each other with a lot of friction, and even after using it for a while this didn't really improve. This cube tends to feel pretty average or good in just about all areas. Nothing about it really stands out as being great, except that it can cut corners really well. It's not a horrible cube, but the way the sides on mine grind against each other keeps me from liking it more. This cube required assembly.
Rating 7/10 (Just my opinion)
*note: I bought a black one
Very loose without popping, and hardly locks up. It doesn't cut corners as well as some other cubes, but it cuts them well enough for me. This cube is also rather quiet. It feels very nice in my hands. The plastic isn't the smooth kind, and many people say this cube feels "crispy". This is my primary cube and I love it. I have heard people saying that newer type D's are somehow different and not as good as older ones. I'm not sure which one I have, but I purchased it after people started complaining, so I'm guessing I have the newer one, but I really don't know. This cube came assembled, and had some sort of lube in it. It didn't turn well at all at first, but I washed it out and lubed it with Jig-a-loo, and it became awesome.
Update: Recently my type D has been locking up on me pretty badly. I'm not sure if this is because it needs to be lubed again, or because I have been getting faster, but it's definitely getting annoying at how much it locks up.
Rating 8/10 (Just my opinion)
Type E (Dian Sheng)
Type E cubes are also called Dian Sheng cubes. When I tried to adjust the screws on this one, I had a lot of trouble because my screwdriver didn't really fit these screws well. Most people say that these are very similar to Type D's, but this cube is nowhere near as good as my type D. It's more prone to popping at tighter settings, and it locks up quite a lot. It probably locks up worse than any other cube I own, including my storebought. It's also much louder than my type D. Seems to have a similar kind of "crispy" plastic though. The one I got has the colors painted on the cubies rather than stickers. There is not much contrast between the red and orange on this cube though, and I found that it really hurt my recognition. Also, the red and orange on this cube are REVERSED from the standard color scheme. That said, this is probably the cheapest cube you will find. This cube came assembled.
Rating 5/10 (Just my opinion)
I loved this cube from the moment I held it in my hands. It feels GREAT. It moves incredibly smooth, and I didn't even have to lube it. It's very "stretchy" and deformable. The cubies are pillowed rather than square. It will not lock up at all and cuts corners at wide angles, however it tends to pop. This cube popped like crazy at first, but after using it for a while and tweaking the tension, it hardly ever pops on me anymore. However, at these settings it's not quite as loose as I would like for it to be. It's still a great all around cube though, and has become my second favorite, right after my Type D. It's worth noting that because of the pillowed cubies, the edges on your stickers might not adhere well if you don't get them aligned just right, and it can feel a bit weird. This cube came assembled, and lubed with something.
Update: After breaking this cube in really well (a few hundred solves), its pretty loose now, and it's not popping on me. This is now my favorite cube... it's pretty much perfect.
Rating 9/10 (Just my opinion)
This cube has very smooth plastic, and didn't even really need to be lubed. Cuts corners well, but it pops really badly for me. Even when I tightened it up all the way, it still popped. It also tends to lock up quite a lot, usually halfway through a turn. This cube feels quite nice, but the pop and lock makes it nearly unusable for me. Lot's of people seem to like this cube though, so your mileage may vary. It comes in many different colors, and I chose the glow in the dark cube. This cube required assembly.
Regarding the glow in the dark aspect (if you choose one of the glow in the dark colors): no it won't let you cube in the dark, because you can't see the sticker colors. The cube does glow quite brightly though. However if you just leave it sitting on a desk or something, then the top part which is exposed to light will glow, but the bottom part wont. It's still pretty neat though.
Rating 6/10 (Just my opinion)
Here are reviews of a couple more cubes. The following two reviews are written by Bomber, NOT by me!
Type A III
The Type A III has quite a distinct feel; instead of having blocks of plastic to hold in the edge pieces they have been replaced with two small tabs per edge. This not only makes the cube feel light but also makes the cube tend to lock up a lot. Like the Type F this cube seems to 'deform' although not in a positive way. Due to the tracks on the edges this cube is not very good at cutting corners, not much more than a Rubik's Storebought.
The Type A III can be adjusted to be quite loose yet still not pop, this makes it quite a fast cube but with quite an unstable feeling.
For more information, check here. This cube requires assembly.
Type A (old)
The first thing you will notice is how soft the plastic is, this has a massive affect on the feel of the cube. The Type A is very smooth and creamy, even more so when lubed well. Most people like the feeling of this cube although is all down to personal taste. Another positive aspect of this cube is its ability to cut corners, this cubes one of the best cubes available when it comes to cutting corners so those with a sloppy turning style should love it! Although this cube cuts corners well it comes with a downside, it pops, a lot. This can be stopped by tightening the screws but it will always be a problem. This cube requires assembly.