Depends on the game~

Kimahri and Quistis are pretty lame blue mages, for example, as their skills are relegated to limit breaks, which is just a stupid-ass decision

In Final Fantasy Tactics Advance, though - that's another story. With a balanced stat pool and the greatest selection of abilities, the Blue Mage can become the best job in the game if you go out of your way to get all the blue magic spells.