I use no AV, just have FF Key Scrambler, then I'd run HJT (HiJackThis) To see if anything is running thatc shouldn't be.
I'd say, you should use AVG Free.
1. It's free.
2. It's not to powerful, it's just right.
3. Easy to use.
Depends on the OS we are talking here...but if we are talking Windows? Id probably tell you Avast Free Edition is good (I use it, and it hardly ever pops up and tell me what I already know its doing ) But, if you are talking paid, I would recommend Norton 360 or Kaspersky, or NOD32. If you are really geeky you can get other programs too that work separately from your main suite and protect other sub parts of your computer. (however most new suites do this for you, but if you go to majorgeek you can find some interesting programs to try out.)