I'd recommend Avast out of those three. It's cheaper than some other products and has better support, and it has a really good heuristics scan. Also compared to most other AVs it has a limited impact on system resources.
I'd recommend Comodo, as it has one of the best firewalls I've ever seen. However, the controls for it are quite complicated, and it would seem better for personal use than for a whole server.
I might recommend Eset's Nod32. But I've never used it myself, it's just been recommended to me allot while I've been here. Their online scanner did help me out of a jam once though.
Symantec products don't seem far to bad. But I can still attest to them eating allot of system resources, as I used to use it a few years ago and from what I've heard they haven't changed.
AVG is no longer recommended by the admins on this site, due to their support of P2P downloads. Frankly I've been using it for a year and a half on one of my computers here, and it's always been a pain, taking up resources and showing false positives. On top of which it's one of the few AVs now that doesn't have a support forum, leaving you to resort to phone or live chat support from an outsourced country.
Just giving my 2 cents. Doubt I really helped much.
Edited by VicVegas, 12 April 2011 - 10:07 PM.