Trib is probably the weakest, followed by Nexus (purely in terms of numbers - the active 3ish heros they do have are all competent and deadly). Then scion, as Ravon is basically the only thing keeping it afloat since Llorenz immed
Empire has strong, strong numbers. 2 hero bards and 4ish hero warriors, plus a hero assassin make for tough times.
Fort is holding its own, though I'd probably put them closer to nexus/trib.
Battle and Outlander seem to have the most solid numbers.
On the fly, I'd rank it:
1. Empire
2. Outlander
3. Battle
4. Nexus
5. Fortress
6. Scion
7. Trib