Avira was my first av, it never caught anything.
I switched ISP and used McAfee provided by the ISP for free. McAfee found a worm & Yahoo AntiSpy (by PestPatrol) found a trojan.
I switched to avast! due to McAfee wouldn't update away from home on my laptop.
Back when I was a Firefox user BitDefender Free Scanner found a trojan in my recycle bin, I cleared my recycle bin & that was gone, it may have been a fp.
Avast! found a trojan, put it in quarantine, that was the last I heard of it.
Since I've been with Opera I've been clean.
I have gotten some warnings from avast!, but no infections.