This is quite an interesting question.
Two of Cicero's most notorious foes squaring off. Perhaps the winner could take on Cicero's other nemesis, Publius Clodius Pulcher. Of course, if all of Cicero's archenemies were involved, I would put my money on Marcus Antonius. Anyway...on to the question at hand.
They both came from senatorial families and had a penchant for debauchery. Verres' family may not have been quite as illustrious as Catiline's, but I'm not sure that would have made him a bit rougher around the edges. Catiline's family had fallen from prominence long before his time, so the two probably would have had similar upbringings.
They both showed a readiness to inflict cruelty. Verres may have more instances of cruelty attributed to him, but his acts of cruelty were carried out by his minions in all the accounts I've read. Catiline, on the other hand, supposedly carried out murders with his own hands.
Catiline was reputed to have had a tough constitution and was capable of enduring physical hardship. I don't believe there is any evidence as to Verres' physical toughness.
They both had military experience, but while Verres' skill in hand to hand combat is unattested, we do have a record of Catiline's performance on the battlefield. Catiline's body was found far ahead of his front line. In order to have fought his way through so many opposing legionaries, he must have possessed at least above average fighting ability.
In the absence of any evidence as to Verres' fighting ability, I have to cast my vote in favor of Catiline. He may not have been able to win the consulship, but perhaps he can win this contest.
