TP
Regular
I, like many here, think the 3x3 is the perfect puzzle. It's simple, yet still challenging. It's a sprint, but it's not so fast that it just comes down to reaction times. As puzzles go beyond the 3x3, very little in terms of increased difficulty or complexity is actually added. It's just more of the same in many ways. The 3x3 captures everything we love about puzzles in a small and easily manipulated package. It lends itself so well to different methods and experimentation. It can be solved OH, feet, or blindfolded. It's perfect. Honestly, I don't see how anyone could ever get bored of the 3x3. I love solving my other puzzles, but I would be happy with just a 3x3. The other puzzles are just a garnish in my speedcubing dinner, 3x3 is the meat and potatoes.
I do think the 4x4 has a lot to add in comparison with a 3x3. Making centers and edge pairs, parity and of course it has everything the 3x3 have since you usually end the solve with a 3x3 stage. Only bad thing is I can´t find a cube I´m content with.
I´m a bit bored by the 3x3, I have no lust practicing it anymore. Solving something well over 5000 times can make anything a bit dull. I still think it´s a wonderful puzzle, but luckily there are a lot off diversity to be had in other puzzles.