I have noticed a trend towards Tarth failing at life.  I have had a few games where they did alright though.  Generally it's Altar, Umber, and Magnar that dominate (for an AI, still miles below me even on ridiculous).  Yithril, Pariden, Gilden, and Capitar tend to be the 'mid-level' AIs and Tarth and Resoln are bottom of the barrel if/when they live long enough to get into the barrel.  Kraxis tends to be a 'wild card', I've had games where Kraxis was among the top AIs and others where he was the biggest joke of all.  But again I've had games that are exceptions to this 'rule'.

They're usually one of the better AI (if one can say that in this game), they usually have one of the highest rating and are usually around to end game. In my experience the weak AIs are the kingdom factions, they always get wiped easily early in the game, It's always a kindgom faction that is the "1-town wonder". Empire factions are always around to mid + endgame & tarth. I always play Altar because I like their at start bonusus.