Found an interesting read here:
http://www.bleepingcomputer.com/forums/topic57265.htmlQUOTE
The Freebies – Alwil’s Avast, Grisoft’s AVG, and Avira’s AntiVir are the scanners that I refer to as the “freebies”, since their entire full version products can be obtained for free. It should also be noted that all three of these scanners are signature-based, and their heuristics are either weak or prone to false positives. AVG, although a popular scanner, is the weakest of the three. It has noticeably weaker detection rates from both Avast! And Avira, and has nothing that makes it exceptionally good in any area. Avast is a decent product. It is only really only slightly better than AVG, but enough so that it is a suitable to use as a decent on-demand or real-time scanner. Avira on the other hand is different. Detection wise, it is a massively better than either of these other products. But it consumes more resources, and isn’t really that good for real-time protection. For a casual user, Using! Avast real-time and Avira as on-demand would be the best set-up among these choices. AVG and Avast have average resource consumption, and ok scanning speeds, and could be used interchangeably for real-time protection (assuming that a different on-demand scanner was used).
Thanks for the info. I'll keep searching for a little while longer before going ahead with the install.