The French aren't bad on the defensive due to all those MGs and the 75mms, but they really suffer from the lack of decent rifles if they have to advance.
I actually really like the Russians. Granted, they're fairly brittle so you have to manage them very carefully. But if you can get into a position where you can field a full brigade on a 3--hex front (keeping everyone within HQ range) you can pour out some serious punishment.
The Austro-Hungarians are a complete mystery to me.
All the weakness of the Russians without their numbers, and atrocious quality.
Every time they manage to disrupt someone, I always imagine that it's simply the Serbians p*ssing themselves with laughter.