I am going to do the campaigns on level one critical mode so if I know the hardest then I would know who to attempt first second and third.

Well, for me, so far Aqua was hard for me to do on lvl 1 in critical mode. Especially fighting against the MF e.e, boy did I die so many times.

I'd say Aqua, just because she's incredibly weak physically and I do not have the patience to grind or play Command Board enough early on in the game to get her better commands, not to mention she is very squishy. As in her defense sucks.

Terra for me, because I wasn't used to the controls yet

yea im finding terra's to be shrot cuase he's sooooo slow!

Terra sucks at dodging, so him.

Probably Aqua for me because she was extremly weak o.e

Terra. I prioritise defense so Aqua and Ven were more easy for me, Terra's defense moves are really bad

Terra of course

terra it wasn't that bad doing aqua

Aqua by far. After the first few rooms on the first world, you're faced with a huge courtyard full of overpowered enemies. Great grinding spot, but still.