The only ones Ive gotten everything for are I-III, VI and IX. IV if you don't count Rydia's optional summons. I and II there really are no sidequests, I is more searching every nook and cranny to get things like Excalibur/Cat's Claw/all mystic key rooms and such. III and IV both have a very limited amount of sidequests, although 100% is a bit of a different matter.

I think the reason why I've done it in VI and IX is just the benefit-cost ratio is just right. The sidequests themselves are overall pretty fun. In X alot of them are redundant and boring, like winning x amount of blitzball tournaments (i've done it) or dodging lightening 200 times. XII, the list just goes on and on, I really don't see myself getting more out of it. for V, VII, and VIII I guess I like to keep that extra stuff that I never got there, in case one day i wanna go for it.