I think this is one of the hardest ones so far. Vivienne is a knight enchanter and a high level circle mage. Winne, on the other hand, while also being a high level circle mage was a Spirit Healer so her focus was more on healing than combat. On the surface you might have to give it to Vivienne. But when adding experience factor Wynne is quite older and fought at the heart of the last Blight alongside the Warden. Her experience in combat is probably far deeper than that of Vivienne's. Not to mention she also took Shale and studied in Tevinter for a time adding to her knowledge base while Vivienne played the political game.
So I think based on her experience both with magic and in combat, Wynne would win between these two mages.
Wynne is older and has more experience, and is a great member in a team as a more support role, But Vivienne is a knight enchanter a mage Trained specifically for Battle, as well as a high achieving scholar admired by many as such. In a battle one on one against Wynne (though I absoultly adore her) would not be able to take on Madame de Fur.