I saw it in 3D and it certainly wasn't a gimmicky 3D film with things coming out at you all the time. So seeing it in 2D wouldn't really matter with this film. Mind you I did get to see
Toy Stroy (1) in 3D.
As for it being the best - that's a tough call. I couldn't pick which of the three TS films I prefer, though these are Pixars best, IMO. It's incredible how emotional the film was especially (SPOILER!) the scene with the old dog, the first time we see Andy, the scene in the furnace and the finale (end of SPOILERS) but that's probably because we can still connect with the sadness of growing up and the passing of time. It didn't help that I could connect with Andy moving away - going to uni not too long ago.
Did everyone see the opening Pixar short too? That was excellent.