I think it's just highest total wins and not how successful you are with them. Could that be right?
I believe it lists in order of most total wins with a specific hero rather than the win/loss ratio(win rate) of a hero. Its kind of understandable that its done this way if you think about it. If you random a hero 4 times and win 3 of those games you have a 3:1 (75%) win rate but if you play a hero 100 times and win 60 of those games (3:2 or 60% win rate). I would say that latter is your more successful hero as you have won more games with that hero even though your win rate is technically lower.