I'd recommend KAV, its very good. But more important is 'prevention' because no av can protect you 100%.
so install only programs you really really need, the fewer the better.
get them from reliable sources.
don't use IE/OE,autorun, screensavers.. and other crap
install a good firewall.
update av signatures
I turn on KAV only when about to run some new .exe, so it takes 0% CPU time.
there is also
this interesting site (and probably more similar). It will check given file with many updated av software. Nice for suspicious files like the ones from p2p networks.
