COM for me, both versions. 

The card system and I have never fully seen eye to eye. 

I always play on either proud then critical with little-to-no struggles until i get to the secret bosses. I remember dying so many times against Vanitas' Remnant and Mysterious Figure in BbS and I haven't even touched the master armours in BbS FM so that's why it's the hardest imo. KHIIFM is a close second tho

Its Com in my opinion because the bosses  have no mercy on you like in other games. 

To me, how hard a KH game is normally depends on the difficulty it's set on.

Well, over the years, it's become to the point that Critical Mode is like Beginner Mode to me, and as such, I have no difficulty with the Kingdom Hearts games at all!

 

A few years back, I would have said that the first Kingdom Hearts was hard when I played it the first time around, and I believe Days was also a tough one for me during the later portion of the game! And let's not mention BBS on PSP, fighting darn Terranort!

 

But as of right now, I have no difficulty with any of the games, not even Union X! I mean, I haven't even spent a single dime on the game, and I'm just about ten missions away from catching up to the story missions, and I have a pretty decent medal collection!

 

Hopefully Kingdom Hearts III comes with a Keyblade Master mode that makes things even harder than Critical Mode!