There is something about rex I don't like. Its like a NFL game where you can custom make players with an overall of 99 and play with them. Rex is like that. He obviously is like a beast. But I feel he is one that didn't "earn" it through a plot or a gradual development. I believe cody is like the smartest, he is in the original series, he is hand picked by Obi-wan, who fights with his brain, tactics, intelligence, and not just ability to fight like a brute like Anakin and his squad, (captain Rex). Cody no doubt-ably learned many things from obi-won, who I think is also one of the top Jedi due to his strategy of learning your opponent before advancing. The dumbest is more than likely the one, I can't remember names, but in one of the episodes of the clone wars, he is always depicted as the clone with "the big guns". And one of the other clones called him out on it, saying, "A big gun doesn't make a big man"