any thing but hacksheild... they suck. They program only looks for detected programs MD5's and strings... it has no actual hack prevention power. It sucks so bad nexon had to try and create their own anti-cheat because they under contract.
Choac - Haven't experienced it too much, so I'm not sure how well it works, but it sounds decent enough (goes with screenshots).
DMW Anticheat - There's a reason why it's no longer used.
HackShield - Easy to bypass.
NProtect GameGuard - VERY easy to bypass.
PunkBuster - It's like you're in a Bugatti Veyron and the anti-cheat is on a bicycle. It'll never catch you (not for a while, at least).
Valve Anti-Cheat - Very efficient, but takes way too damn long.
Virtual Shield - So-so. Not too bad, but whatever.
Warden - Little time to catch someone, but only because there are very little people that hack on WoW. If 1/10 of the people did, this wouldn't be as good.