What are the different between 2k11 2k12 2k13?

It depends on what platform you're playing it on.

If you're playing it on either consoles, 2k12 is superior in nearly every way.

If you're playing on PC, 2K12 presents several severe limitations compared to 2K11. First and foremost, developer support is rock bottom for 2K12 on PC, having only received the first patch of 5. Second, mods in 2K12 must use exactly the same resolution textures, otherwise it will break the game. This makes a huge impact on the quality of mods in 2K12 and in fact leaves 2K11 the capability to look much better on PC with high resolution mods installed. And third, the account issues that have plagued 2K12's online mode seem much more prominent on PC.

2K11 also happens to be much easier to play with just a keyboard, where as 2K12 is much more reliant on stick controls to produce even the most simple moves. (Hot-stepping for instance)