If AVG was doing that to their systems they were using it incorrectly or they got a bogus copy.
Agreed. I've been using it for several years with no issues (and no viruses). While it has fattened up in the latest version, if you are running a halfway decent rig you'll be fine. I've also uninstalled it with no issues. There are a couple of other free ones out there that I've heard are decent, but AVG has not given me any reason to switch. There are a couple of things you may want to tweak on it, but hey it's free!
MaximumPC recently recommended AviraAntivir
AntiVir's biggest strength lies in its detection rate. It's the only scanner in our roundup to triumph with a near clean sweep during Virus Bulletin's latest testing, and it did so without reporting any false positives. That's impressive. AntiVir performed equally well in our Lab, as long as we didn't attempt to install spyware or hijack the browser.
If you can live with the popup ad AntiVir forces you to view each time a scheduled update is performed, you'll be rewarded with a potent, no-cost AV scanner. Move over AVG, we have a new favorite freebie.
So, that one may be worth a shot if you can live with the popup.
BTW, Ubuntu is a flavor of Linux