I got Team Fortress 2 on Steam yesterday (it's free now). The VALVe intro loads up, then a loading screen, then it crashes. I looked on Steam Support, found the programs that could interfere with Steam, and with a green star next to it: AVG. If I uninstall it, Malware could come flooding in. How do I play TF2 without installing AVG? I have no other Anti-Virus programs.
This particular set of benchmarks and tests show that the best free AV software is Avast! Although this is a particularly extensive report, choosing the right AV software for you all comes down to personal preference.
I can, however, confirm that Avast! works fine with TF2.