I'd go further and say it's often impossible to run more than 1 AV (resident.) Conflictions are likely (my experience from a while back) and I've read from a few experts that the level of protection can actually end up being less.
I've used AVG, Avira, Norton, and Avast. I prefer Avast, and believe it has, through its configurable options, webshield, and boot scan (currently u/s but should be fixed soon) a better level of protection.
Personally, I'd uninstall both of them, (be disconnected from the net) run a disk cleanup with CCleaner (or similar) restart, and install fresh the one you want to use.
If you choose Avast I doubt that you'll be disappointed. I find the forum support excellent and fast, the program excellent, and have been pretty much malware free since using it. (With a few other security applications.)