-==MOD==-, ClamAV is not really needed with Ubuntu, the whole idea of having a so called anti-virus with Linux distros is not to protect Linux it self, it's to protect Windows users, for example, if you have an audio file binded with whatever in Linux, it's useless, but if you share it with a "Windows" friend, he'll basically get pwned.
ClamAV, or any Linux anti-virus is to help you, help your Windows friends not get infected, which is a big "lol" actually, Linux developers are even thinking about Windows people, Linux ftw, Ubuntu rules all.
I had ESET NOD32 in the past, always thought it was really really good but at one moment it left some trojans in. I uninstalled it and never used it again. Now I use avast which is doing a great job!
Avast is much better than NOD32, the trojan problem with NOD32 has been known for awhile now, it "catches" most malicious files, but it's terrible with trojans and has no "suspicious file behavior" tactic, at least not a good one.
Kaspersky (KIS), after it Avast, if for some reason you just hate both, then go with Avira, other than that.. don't bother.
But hey, that's just my opinion. :P