Hmmm... Decisions, decisions.
Statistically, the most sound of all of them all is Caineghis. However, I've had all of them get insane high stats, so it really comes down to personality (though for utility, I think Caineghis is the best, for the final chapter in any case, with Tibarn and Nailah at a close second).
In ways of personality, here's my favorites in descending order:
Tibarn
Nailah/Naesala
Caineghis/Kurthnaga