That's not an easy question. Here are the ones that have stood out this year - in no particular order - from the teams I've seen so far (mostly Western Division):
Danny Syvret (London) - from my understanding, he's a great dressing room guy, and very much a "team first" attitude. This was a surprising choice for London, but I think it was a good one.
Tie - Ryan Callahan (Guelph)/Brad Richardson (Owen Sound) - again, both have a "team first" attitude, both lead by example, and the "C" rests easily on their shoulders.
Mike Richards (Kitchener) - may be a homer pick (go ahead and flame if you want), but his leadership stood out to Peter Deboer in his rookie year. It's visible every night on the ice, and I've heard the same from fans of opposing teams.
Don't know if he's in the top 3, but Oulahen from the Brampton Battalion would be the most underrated. He has his team in first place in the OHL Eastern Conference and would probably check to a standstill all of the other captains that might be mentioned here. The players know their opposition the best. Just ask the likes of Locke, Stajan, Brent, O'Sullivan, Carter, Richards, Eric Stall etc. who they hate to play against.