A lot of times I force AIs to surrender. When I do, I can see what they've picked as their traits when they level up. There doesn't seem to be an any strategy to their picks or maybe I'm missing it. They just seem to incrementally pick, or have a great preference for at the very least, the traits on the "General" tab.
Consider this example
Procipinee decided to pick every trait from the general tab she could. There were no picks on her assassin class.
This seems to be a trend. Here's Warlord Verga from the same game...