I have become increasingly happy with my cube4you MegaMinx. I had the problem with tiles popping off, and it still happens. But I've found that regular white glue (Elmer's) works better at holding them on than does super glue. Surprising, but it has been true for me.
About 2 weeks after I got my first one, I sanded down the bumps with sandpaper. It was very tedious and painful to do - I'd recommend using an electric sander if you can get one - but I got the bumps about half sanded off (it took me about an hour to do that). There are still bumps, but not as big as before. So I still get the satisfying click, and I agree with abbracadiabra that I like it that way.
Then, this weekend, I lubed it using CubeLube (Johnson's ShineUp). And I could not believe the difference. Now it turns fantastic, and I feel like it's far less likely to pop tiles off as well. My times improved by a whole minute on average, instantly.
I don't think I have as many reservations as abbracadiabra about the Meffert's MegaMinx, but I still must admit that I feel like I've spent a lot on puzzles, and my Chinese MegaMinx seems awfully nice now after preparing it, so I find it hard to believe it will be worth an extra $28 just for the minor improvement that a Meffert's would probably be. My Chinese MegaMinx is awfully nice now. Then again, I am still very slow at the MegaMinx (about 4 minutes now), so my opinion probably isn't worth all that much.