Okay, so 103(-or so) Viners got in before me, but my vote MATTERS, damnit!
I'm going to run that although it would be a close call, I think that Colossus would take the win in the end.
Aric is a barbarian who has only known war and fighting his entire life and basically has multiple centuries of knowledge worth of combat victories under his belt, partially from Romantic times and later during the present, so he is no stranger to fighting. He has the alien armor, which grants him increased physical abilities, flight, energy projection etc as well.
Piotr has invulnerability and greatly increased strength.
Aric is not about studying his enemies for weakness and exploitation. Whereas he does have greater mobility advantage and could use this to his advantage, his style seems to be run in guns blazing, fists flying, shoot 'em all and ask questions later.
Piotr while stronger physically, cannot chase into flight or move anywhere near the speed that his opponent can.
Both start on the street level and aware of one another. Colossus hurls a bus and XO barrels straight ahead, smashing through the airborne projectile. XO shoots at Colossus while closing the gap, but the organic steel repels the energy harmlessly. When it comes down to the two being at melee range, XO definitely has the lion's share of the speed, but Colossus has enough sense to anticipate where XO's strikes are taking him and plant just one well timed blow: not enough to kill, but enough to incapicatate and claim the win.
Even if XO wanted to try and make an airborne assault, he has no way of actually harming Colossus, and as his only other method of gorilla tactics would be to punch through the street level into the subterranean sewers or underground train lines, neither of which are likely and both of which would end up being either a case of retreating or another entry into brawling range. I still do not believe Aric would take either of these courses, however, as his barbarian nature isn't about the "dirties, sneakiest under-handed-est" fighters being the ones that win, but the one who is the strongest being able to overcome his adversaries. The ballte isn't won by Colossus because he is stronger, per se, but because of his ability to withstand attacks and think and plan to counter-strike.