Warrior: Fenris followed by Cassandra. Fenris because his Lyrium tatoos give him too much of an edge over all the other close calls. Warriors are closer to each other than other classes. He edges out Cassandra because his Lyrium qualities give him the ability to phase into the fade momentarily, and that is all the edge he needs to win against even a seeker.
Rogue: Zevran followed by Cole. Zevran edges out Cole because Zevran has more awareness of reality and has the skills of an assassin to be able to beat any of the other rogues. He beats out Cole because he can outwit Cole 1v1. Cole's advantages will be hard to use against an assassin like Zevran.
Mage: Morrigan followed by Solas (before absorbing Flemeth). Assuming Solas is still weak from slumber, Morrigan has the most arcane knowledge out of all the mages. Vengeance Anders is a close 3rd, but loses out to Morrigan because Morrigan has more knowledge of the arcane than Anders. Vivienne and Wynne and Merrill are all very powerful, but cannot still match Morrigan in knowledge. With mages, the more you know means the more powerful. Anders gets a quantum leap due to Vengeance, but that sheer power is limited by his lack of depth compared to Morrigan. If Solas is strong and not weak, then he will be the best.