Clamav is as good as others in catching virus. Problem is that it only detects, does not clean. Also, it is supposed to be good with new virus. But never used in production environment. Only on test server.
Clamav also has a paid product which has cleaning ability.
Hmm! I guess for a File or Mail Server configuration what you really need is a detector (scanner) only.
Cleaning is pretty much a 'recover after blow up' situation which I guess any standard windows AV scanner like AVG should be good enough in case ClamAV fails.
Rishi