Well IMO... OHL probably has the most skill top to bottom, their bottom 6 will have more skill than the other leagues do. Its the softest and least physical league of the three. It's more insular, more of a planet Toronto type feel. There's less parity in the league too, more haves and have nots. Less travel, they don't experience the road trips the other two leagues do. It's the most pampered and gets the most attention.
WHL is the more rugged defensive league. The most physical, most fights and hitting but more NHL style structure and systems. It's why they seem to turn out more defensive players and defensemen.
You didn't ask but Q is the most offensive league (though it's not the beer league offense that some people liken it to, OHL scoring is just a shade behind). It's a more passionate, intense game, which can lead to some huge hits and physical play. Lots of small, speedy skilled players. Turning out more defensemen than the OHL now (look at the WJC team, it's mostly Q defensemen).
I personally don't think there's a "better" league where you'd prefer a player to come from or that makes their stats look better. It's all about the type of team they are on, the role they play that gives it context. The OHL is my least favorite of the three and the top heavy nature of that league can skew stats. Q is probably my favorite, I like the players and the game best in that league but I appreciate the structure of the WHL, there's a lot of good teams in that league. Q goaltending gets crap because they have some weak ones but their top goalies are some of the best, same with the W. OHL goalies are more average to meh.