Tommy's best feats were taking out an entire mansion of mobsters, and...actually, I think that's the best thing I can come up with right now.
Meanwhile, Carl canonically broke into Area 51 and killed his way out of it, shot down a gunship piloted by a paranoid, combat-trained CIA agent, and killed several armed Vietnamese gang members on cargo ship while starting off with nothing but a knife.
CJ FRA. He's been through things an ordinary thug shouldn't be able to go through. Blasting through thugs, police, and the military, sneaking through their base, piloting a jet for the first time and actually managing to defeat two other jets who obviously had training.
Let's all face it GTA San Andreas is the best GTA game.