Hey astrofs,
CAVS cannot scan your gmail messages:
http://forums.comodo.com/help_for_comodo_antivirus/which_mailclient_works_best_with_cavs-t11649.0.html;msg82650#msg82650 (for more info read the whole thread - I learned a lot)
IMO, if you want your mails scanned by your AV, you should stick with AVG for the moment. It also has better detection rates. However, if you don't use CFP v3 with HIPS, or have installed any other HIPS, then the HIPS feature in CAVS might also be something to consider as it provides a great deal of extra protection and is, again IMHO, much more efficient than any heuristics used by the more popular AVs.
So it's really a question of your needs.
What I'm really sure of is, however, that once CAVS v3 will be out (and out of beta) you'll hardly find a better AV on the market - free or paid for. So even if you stick with AVG for now you should keep an eye on the development of CAVS as it's getting better by the day.
Just my 2 pence,
grampa.