This is probably a well-known subject, especially since the MaxPC article on security suites a few months back...
We had TrendMicro on our server from when it was purchased, and now (with heavy usage and number of users) am having nothing but trouble with the program.... Server runs fine when you disable TrendMicro, but with it enabled, it runs so darned slow (I mean, the speed between the client and the server is so decreased it's not funny).
We'll be switching apps soon (when the subscription expires), but still.... It used to be a decent AV app for both desktops and server, but lately has gone down hill (now, NIS has gotten better as time progresses). At home, though, I personally like ESET (although it does have a problem with my banks website for some reason--that's my only gripe about ESET).