My brother likes the Spanish, the Scutarii are decent. I personally don't like the use of Bull Warriors for my own because I question their historical reality. But that is just me, I try to factor realism in instead of just playing for fun. I don't use Druids, despite the fact that I have seen firsthand how useful they can be (I used to use them).

It seems Dacia does not get much mention, probably in part because you have to mod to get them, same as Spanish. It seems to myself and my brother that Dacian Warband seem to fight better than standard Warband, though I doubt that is actually the case. Then again, maybe since they are supplemented by Falxmen instead of Swordsmen, the battle goes better for them, so they don't rout as quickly. But Chosen Swordsmen and Chosen Archer Warband? That would make for a tough force, especially because they also get Barbarian Noble Cav, who are decent as well.