I've used AVG with no complaints (..well, except it used to use high resources years ago and so this may not be the case now). Avira free is still on my XP system, and turned out to be surprisingly good for a free AV! (which is why I chose it).
That said, for both our Windows 7 & Windows 8.1 systems we've opted to use the native, Microsoft Security Essentials & Windows Defender AVs respectively with Windows Firewall because (IMhO) they give amazingly effective protection. Ultimately, you should go with what you decide you feel fulfills your needs; and the best way to do this is similar to when one buys a car. You test drive them first to figure out which is right for you. Good luck!