Thal has a huge military, as Kalixta has learned the hard way, and a strong culture. Melhed has an excellent military, fine regions, and a lot of hate for Thal. They have also, thus far, held to a higher standard of war, but Thal has a lot of land and a lot of hate and likely the biggest army in Bel. Both have infiltrators doing nasty things and some nobles have already been executed
You might find a particularly interesting game in joining one, then deciding with you would rather play with the other.
That being said, I'm biased, go Melhed!