There is a lot of hate for FFXII.

FFT is not widely regarded as the best FF ever, so it's underrated.
True, but it is rated fairly appropriately by the people in the know

I'm going to go with FFIII. I always overlooked it as being primitive on the level of FFI (don't get me wrong, I love FFI. But it is still a game made in 1987), but playing through it I felt the only thing that separates it from modern titles is the lack of character development.