Final Fantasy Tactics. I can't think of a single class that wasn't useful in that game, and to me, it really struck the finest balance in general for all the abilities. This was one of the few games I've played where it actually helps to do more than spam things like Firaga or Ultima the entire battle. There's a lot of strategy involved in using magic in that game (not to mention the fighting in general). I'm surprised FFVIII is in second on that poll though, as it'd be my least favourite hands down. Don't get me wrong, I liked the Junction system to a certain extent, but the spells in that game were generally weak (weaker than regular and special attacks anyway), so there was next to no incentive to use them, especially since relying heavily on magic meant lowering your stats. My opinion might be different if they had struck a finer balance between the usefulness of the spells when cast and when used for junctioning.