IMHO - I have tried many virus checkers over the years, My current one is Avast and I have been using it for nearly a year now and I find it the best yet. AVG let me down once and I have never trusted it since, did download the trial to norton but a virus disabled it
so that got binned too... I have not tried Anti-Vir as suggested by TECHGUNS so I cannot give my own views on the software, if Avast ever lets me down then that will be my next port of call.....
Avast is free for personal use, if you wish to try it out you can download it from
here. What ever the choice you make - just make sure that your old virus checker is disabled before installation and running of a new virus checker as this can lead to slowdowns and software conflicts. Also make sure you manually UPDATE straight after installation and then UPDATE manually at least once a week, it is no use having a virus checker with out of date definitions