Gladiator's confidence isn't like Hulk's rage...he's usually extremely confident, even when he's losing or evenly matched sometimes. It doesn't wildly fluctuate a great majority of the time.
Gladiator probably has more raw power. Thor has some magic, roughly equal physically, and the whole "god" thing going for him. But if Gladiator is smart about the fight, using his speed and such (which is a huge advantage for him) he should win. He might not kill Thor, but beating the tar out of him counts as a win too.
Gladiator.
-DM
Yeah, Gladiator kept up with someone who was fighting 100x speed up light.
Glad's confidence deal is hardly worth mentioning, the guy doesn't freeze up at the first sign of danger.
Gladiator could probably lift Thors hammer, he's pure of heart and all that jazz.
Anyways, it'd probably be a tie unless Glads speed blitz him, then it'd be a massacre.