Good evening! This will be likely an unpopular answer. The first thing we have to debunk is the Hollywood myth of the gladiator as this invincible, unstoppable warrior who fought to the death for the mob. The reality is much less powerful, as gladiators fought bouts that were refereed and judged. They were basically too expensive to allow to die, and generally fought to entertain with strangely mismatched and balanced equipment. They did not fight to kill, normally. On a random note, Gladiators also tended to be fatter. Legionaries, on the other hand, fought, according to Polybius, Vegetius, Tacitus, Cowan, Goldsworthy, Fields, James etc.....in more open formations, with anywhere from 3 to 6 feet of space between each soldier. They were organized but in looser order, so they actually fought with tremendous individual skill. Motivated by virtus, their manly, soldierly virtue, legionaries could act like absolute berserkers, as Caesar and many others wrote.They could be expected to mass closely to repel cavalry, for example, but in general, against infantry, open order was the norm. Heavily armored, and equipped with heavy impact weapons such as the pilum and Gladius (which means sword, NOT short sword,) the legionary/Auxilia/Praetorian had one purpose, and one purpose only: kill the enemy. They didn't care about looking good. They wanted to kill their enemy and go to lunch. As for who was better, Tacitus settles that one easily. Examples include two battles against Praetorians, where the guardsmen massacred hundreds of gladiators quickly, the Battle of Cremona, where Batavian Auxilia foot and Roman legionaries shattered a body of gladiators on contact, and the Treverii Rebellion in AD 21, where again, Roman legionaries defeated gladiators with relative ease. In my doctoral studies, I genuinely feel the army produced better killers than any Gladiatorial school, and that includes the Third Servile War.