I didn't pick Allan during DKS. I remember how crap he was during Ego and it's Barbatos who is the better alchemist.
Actually, the only difference was that Barbatos' quests resulted in one extra skill point, and hat Barbatos needed you to give up the Alchemy Amulet, while Allan needed the Potion of Wisdom. Not a terribly huge difference, and Allan gets you the unique Allan Brew formula, too.
