Yes, you do need to uninstall AVG completely. AV products are sometimes hard to uninstall completely, so use the remover tool from
here to do it rather than just relying on removing it using the add/remove programs list.
I have been using Avast for several years now, and I have never had a problem with it. It does require you to get a new serial number by email every year, but that's about the only annoyance if you can even call it that. Absolutely rock-solid and you sometimes forget it is even there.