As terrible a teammate as Owens was, there's a reason he's a legendary WR. He had a great work ethic that he learned from Jerry Rice, he had freakish talent when it came to speed, he could run all the routes, and even if his hands aren't better than Dez's (I've seen him drop some easy ones far too often as well though), Owens' hands weren't bad.
Like others have said, Dez is a more physical WR with amazing leaping ability. I would like him to become a little better with his route running, but he has improved a great deal since coming into the league. That's really all you can as for with a player, to just improve each and every year. I won't count Dez's yards against him, we just spread the ball more than most teams in the league, the fact that Dez gets 80-90 balls a year is incredible.
Owens wins on talent alone, but what separates Dez from Owens is the attitude. Owens, just like Moss, could have been better WRs than Rice (Especially Moss). Sadly, he was and still is an egomaniac that could never build true chemistry with a QB. He talked his way off multiple teams until the day he retired.