Since thieves have 132/135 AC without any AC items, you don't really need AC that desperately. The easiest would be to make 2x Force + 1 Distant, Force + Force + Desire or Force + Desire + Distant. Simply ice blast your enemies down with invisibility. The easiest and cheapest way to own everyone.
You should only use EX ice on archers, low ac thieves and people without defense buffs.
You should consider making one AC or Smart and one Evasion item to survive as a turtle when you're pepsied/slowed/stunned/blinded or when you want to pepsi as a support.
I'm talking about maze and war situations here of course, where teamwork and potion mastery matter.
Good luck and have fun. Thieves are easy enough to play efficiently, but if you master them, they're absurdly powerful. They have almost everything.
