Umaro and Gau are both beasts when used correctly that should be main stays in your party. The other I would say late game is Setzer. And then have Edgar or Terry in the front. Honestly they make the game extremely easy in the world of ruin. Umaro really shines in the world of ruin in Kefka's tower of magic. Just be sure to be able to cast Life3 sit back and let him do his thing. Once Setzer can grab the fixed dice give him an offering and a genji glove and let him shine. Gau doesn't need every rage from the velt, but you can grab some powerful ones there that will make life easy with very little farming.