I've actually been going over the four primary circle choices myself to figure that out. Detereorating Corrosion is starting to look less enticing. It's the most damaging, and there are a lot of decent debuffs, but something is rubbing me the wrong way.
Searing Flame has some good effects like dazing and adding a good amount of damage to melee attacks, but only a couple of us will benefit from that much. I think I'll probably scratch this one off the list.
I like the formulae in Perfect Freeze, it's definitely a contender.
Shocking Current is off the list.
So far it seems to be down to Detereorating Corrosion or Perfect Freeze. Really not sure which to go with right now. :/