1. Warden. I liked warrior Hawke, but really he wouldn't stand a chance against my bloodmage Surana.
2. Aveline. She's more badass than Alistair. Alistair would probably underestimate her because she's a woman and that would be his last mistake.
3. Sten. He is elite Qunari Warrior. Fenris has the lyrium markings but unless he can take Sten by surprise I don't think he is a match for him. On the other hand if someone like Alistair can defeat Sten in a duel... maybe Fenris' chances are not so bad, after all. He is more determined and his anger fuels him.
4. Morrigan. They are both very powerful and probably have somewhat similar training, but I think Morrigan is more cunning and might just have a few more tricks up her sleeve.
5. Anders. No challenge. Justice/Vengeance will crush Wynne's spirit friend and without it she is just old woman who has wasted her gifts dancing to the Chantry's tune.
6. Leliana. She doesn't even have to fight Varric - she could just send her spies to poison his wine. If they did fight one on one she would still beat him. She learned from the best.
7. Isabela. Zevran is too easily distracted...
8. Arishok. Shale is more chaotic and can do lots of damage to her environment, but golems are also clumsy. Arishok is elite warrior with deadly focus and lots of minions.