This is a tricky one but I'll try to break it down
The only real feats that we see ozymadias accomplish is: A. Defeating nite owl and rorschach B. Catching a bullet C. Temporarily out-smarting Dr. Manhattan
There have been more feats accomplished by Oliver over the course of the TV show, but to make it easily comparable, I'll limit it to just three: A. Stabbing himself with an arrow to "kill" Malcolm Merlin B. Defeating deathstroke C. Surviving being stabbed in the chest and kicked off the side of a cliff and staying there in the cold for at least four hours
Realistically, they're both very well matched, it's arguable that ozymadias would win simply because he defeated rorshach and nite owl by himself, however this becomes a question of the comparability of Oliver to rorshach or nite owl
Since we're basing our opinions off the film, it's obvious that nite owl and rorshach kick a lot of ass, however, none of the ass that is being kicked quite stacks up to some of the people Oliver has taken down
I would compare this fight to Olivers conflict with ras al ghul in season three of arrow, the way that fight plays out is similar to the fight between ozymadias and rorshach feat. Nite owl, however, Oliver is one on one and and later rematch takes place where Oliver kills the head of the demon
Now this does not mean that Oliver would win this fight either, I just simply don't believe that ozymadias would have the sheer power to hurt Oliver enough to kill him, save catching one of his arrows and stabbing him with it, however, (sorry I've said that like nine times now) that brings in the question of what weapons and armour do they have
In an unarmed match, it would be easy to say that ozymadias would win based on his fight with you know who, but as we see in arrow, even un-armed, the arrow is a force to be reckoned with, (remember death by poker in season 1?) Most of Olivera fights aren't simply him shooting arrows at people, he fights hand to hand just as much as ozymadias
Then we have to bring up the question of physical fitness, Oliver gets trapped on an island for 5 years when he 18, he returns at 23 to take over his father's company, the events of season 1, 2, and 3 all take place over the course of three years, this would put Oliver at most at 27, ozymadias on the other hand is the third oldest member of the watchmen at 43 during the events of the comic book (sorry I cheated)
Ultimately I cannot decide the winner, I say it's a draw