At that point in the game I think I went Shulk, Dunban, and 7 (don't want to spoil it for anyone that might stumble onto this post). Those 3 have the best DPS in the game and can do well. I experimented heavily with Riki and Melia as well, but they usually took a bit more finesse. By that point you should be able to kill most enemies very quickly, so Riki's DoT skills sort of fall out of favor.