That depends on whether you want a free AV, or a paid AV. AVG is a good free option, but like all free versions, its detection rates are not quite as good as commercial AV engines. This site has results of periodic AV engine tests (on the best commercial versions of each AV engine IIRC), very useful:
http://www.av-comparatives.org/
Avira and NOD32 tend to come out on top, especially in the proactive tests (which test detection of viruses with old definition libraries, testing the ability to identify new viruses).
As for removing Norton AV, Symantec bowed to pressure and released a complete uninstaller tool:
http://service1.symantec.com/SUPPORT...05033108162039