Actually, it's all up to you, I loved Cyan, and in fact could beat the entire game using only him. You only need to level up 4 characters really. Even when you split parties, you can have on group with the moogle charm, making no random attacks, and the other groups have 2 of your good characters.

My best party was Cyan, Sabin, Edgar, and Gogo my first time through, the only thing that changed was Gogo rotated out for some other character. But the best weapons aren't that special anyways, considering Edgar does max with chainsaw, sabin does max with bum rush, and Cyan does max with dispatch (level 1 swd tech).

Good trick with Cyan though is to teach him quick (spell) and use it, he'll get 2 attacks without anyone being able to do anything, so he can fill his swd tech bar to 7 without anything happening. That trick works, and then of course he can attack a third time, in which case you use quick again, and he can beat the enemy without ever getting hit. And if you're running low on MP, cause the spell costs 99, just drain it from the enemy with one of your turns. I literally never got hit on the final boss using this trick!