The main difference I see, besides the Pokemon available, is that in White 2, you can catch more Pokemon in White Forest and get an easy mode when you beat the main story. In Black 2, you can buy rare items in Black City and get a more challenging mode when you beat the main story. Me? I prefer White 2 because of the Pokemon availability and I can unlock challenge mode by having my friend send me the key for it, since he has Black 2.