I have my own choices and dis-likes so..
If you want free,user friendly,very good preventer,constant product improver choose avast! I use avast on my PC itself and i have test it everyday with malware packs from malwares.pl and many more places detection rates have risen since last version either way there is no way to exact detection rates as there are un-countable pieces of malware out there..My opinion is the same as ZOU1...Flash up a VM and test it against links from MDL,malware black list,VXVault and minatour analysis...and you will realize what we both mean.
At MalwareTips everybody has same opinion on avast's protection skills..detection rate is around 80 to 85% in my tests against a lot of packs including from here..sometimes VPS late releases causes a sudden drop down but comes up again in next update.watch a review: http://malwaretips.com/Thread-avast-Internet-Security-7-Test-biozfear14
if u want non user-friendly,HIPS based,anti-malware time bomb choose CIS.
Paid choices- KIS,Norton and the list goes on and on.
Avira-It slowed down my pc boot time and the program randomly crashed in between...and it told me to remove COMODO FW/D+ and MBAM ...so i had to go back to avast! tested avira with a 0-day fakeAV URL and it failed...tested with same URL against avast and it blocked it..avira has a great database with malware that has been around for a few days...but it lacks a URL blocker that most AV's use against 0-day Malicious URL's and i have seen avira web guard is totally dependent on signatures so its practically useless installing the web guard with that annoying toolbar which i hate!!avira is yet a very good product though and can give other AV's a run for their lives in many cases
Remember: there is no best protection except you and b) your brain