Dunno about 'upper level', I have a level 55 SK who's a bit light on AA's. He currently has gone with Rallos Zek, but is seriously considering swapping to Bertoxxulous now that he has appeared, mainly due to the disease stuff.
Choice was mainly a RP decision, picking the most appropriate. I can't say I really use the deity spells on any of my characters though.
You might find Ten Ton Hammer's
Choosing a Deity Guide helpful.