While clearly not the favorite Final Fantasy character, he definitely deserves it the most. The Black Mage has been in nearly every Final Fantasy game, and several other games. While I can see why people want Cloud Strife in Smash Bros., I don't see him as the single character who represents the entire franchise, considering he wasn't in the first 6 Final Fantasy games. Also, the Black Mage could easily have a more unique moveset.
I think it's fair to say that the Black Mage would be loaded with projectiles. He could have a few physical attacks with his staff along with maybe a few basic punches, but for the most part, he could have a wide range of magic attacks.
These are just a handful of moves he could possess. He also has many new moves from the newer games. However, I think he should have mostly older game material, but mixed with a small amount of newer moves.