Well, I'm using Symantec Anti-Virus Enterprise Edition.. Not free, but no activation either, and if you know how to get it, you can use it for free.. Although illegally..
I had experience with AVG, then there is also NOD32 and Kasperski.. They measure from top to bottom like so, Kasperski, NOD32, Symantec Enterprise AntiVirus, then AVG at the bottom..
I prefer Spybot to ad-ware and that's just my professional preference.. If you choose ad-ware that's your choice I don't hate you or empose Spybot instead.. Though I recommend it more than ad-ware..
There is also Microsoft Windows Defender.. In my book it's in the very bottom of spyware/adware defending utilities.. If you have that along with ad-ware or Spybot, use only one.. I recommend spybot..
Worst anti virus you could get is Symantec Norton AntiVirus.. Professional or Personal editions, they are big and bulky and take a lot of system resources.. While the enterprise solution is light and quick..