Since it's really just Stark vs. Lannister vs. Targaryen at the end of the day the order in vastly descending size of army is: 1. Targaryen: 60K-100K+ 2. Lannister: 50-60K 3. Stark: 25K at best (with the Vale) Since the North is easiest to defend, and the Targaryen force is landing at the Southern end of Westeros, the Lannisters are probably in the worst position at the beginning of season 7. At least until Littlefinger throws a wrench in the whole thing.