Basically what im asking is... What was the hardest part, for you, in Final Fantasy 10?

For me it would have to be the monster arena. Its really hard for me lately to kill one of the creations lol im trying to get the creations to kill Tidus and then he'll be in overdrive so i can get him to use Blitz Ace!!

Is Blitz Ace really good?

Since everything can be beaten with Yojimbo, there is actually just one difficult monster in the whole game:
Shinryu

since you can only use Wakka, Tidus and Rikku. So it's just to start spheregriding (I didn't primarly use those characters the first time I played)
Thankfully, it's in the monster arena, so it's possible to just leave out of your story