Which game does Magic feel the most rewarding to you?

[Wolf Kanno]

I'm actually gonna say IX, for being damn powerful at all points in the game and every new tier of spell being felt very hard. And Spellblade is just all sorts of great.

I can agree with this. I still feel Vivi is the best pure black mage in the series from a build stand point. The fact he's IX's best damage dealer helps as well.

In terms of an entry where I felt magic was not as useful, eh it depends...

I can agree with Lord Golbez that magic in VIII, when used conventionally, is incredibly underwhelming. Likewise, I agree with Fynn that VII's magic is often just overshadowed by summons, enemy skills, and good ole fisticuffs. I also find magic underwhelming in XIII, but that's likely because it functions differently from a usual DPS thing so it feels like an after thought. With that said, I find magic the most underwhelming in entries where melee options tend to overshadow it.