Sphere Break is by far the hardest of the listed. Better make sure your Math is in check, especially if you want the Lady Luck dressphere, which just so happens to be one of the best dresspheres of the game. Of course, it also depends on the opponent.

The piano one is super easy, and so is the wall one (the map literally says which one is next, not to mention the it is opticional).

Passwords are also fairly easy, though I sometimes have some difficulty in understanding if the number is a 0 or a 6 or someone like that because of the font and positioning.

The platform one is easy too, plus it's a great place to grind.

But all puzzles of FFX-2 are relatively easy considering you'll want a guide by your side so you'll get the Perfect ending, and the guide will explain everything. The only puzzles the guide can't help you as much is the more randomized ones, like Sphere Break.

I always had trouble with one of the Lightning towers in the Thunder Plains.