Kingdom Hearts 2 is a good button mash with some interesting endgame fights in Final Mix.
KH1 feels a bit more tactical and heavier.
Both are good but KH2 takes the crown for the sheer amount of content.

Dare I say, KH3 ReMind bosses are possibly the best. Finally beating Yozora with all pro codes active, I don't think that level of euphoria can be topped.