I think overall 96 is my choice. It's got Geese and the other boss team folks and many other cool things. 97 seemed lacking with the ambient background noise in lieu of music, it didn't get my blood pumping as much as good music would and just felt incomplete to me.
KOF 94 and KOF 2000 are other key favorites of mine. And frankly, I think KOF 2003 has a lot going for it with a huge amount of new characters, costumes, other graphics, and the tag gameplay, it was a good breath of fresh air in the franchise. Never played any of the ones that came out later on atomiswave or other non-neo hardware...