Norton is the biggest example as to why paid versions dont always mean better versions. Norton is the worse AV u can possibly install on ur computer( as bad as the free AVG)
There is no BEST antivirus free or paid.
The best way to keep your computer up to date, and free of any malware/spyware/viruses, is to have the best combo of programs: a good antivirus, a good anti malware, and a good disk cleaner.
This is the combo i recommend having and runing once a week.
Download AVAST from
http://download.cnet.com/Avast-Free-Antivirus/3000-2239_4-10019223.html?tag=mncol;1
On the lest side, click DOWNLOAD NOW. Install, run it-remove found threats.
Download Superantispyware from
http://download.cnet.com/SuperAntiSpyware-Free-Edition/3000-8022_4-10523889.html?tag=mncol;2
Download it,install it, run it. Perform Quick Scan. Once scan is complete, click Show results-check all threats found and click Remove Threats.
(As a small PS- i choose Superantispyware over MBAM(Malwarebytes), simply because MBAM is not what it used to be, and Superantispyware actually cleans up where MBAM failed)
Download Cleaner from
http://download.cnet.com/CCleaner/3000-18512_4-10315544.html?tag=mncol;1
Cleaner is a very useful tool that cleans your computer of temp files, history and cookies. Its also used to fix any registry errors.