I want to know the best anti virus s/w till date in this world
I've tried many and downloaded very good a/v s.w from downloads (http://www.downloads.com) but I want even better s/w's

Best is a relative term and changes depending on who you ask
Overall though it is best to avoid these "all-in-one" security suites as the cause problems and don't bother with Norton at all.

My favorite antivirus software is actually the free Comodo Antivirus (http://freeitnernetsecuritysoftware.com/free-antivirus-software.htm) but if you want to spend money on a commercial item then Trendmicro just got a great review in a highly respected consumer's reporting magazine ;) . If you are interested in the Trendmicro product I would probably go for their security suite.

I myself always like Avast antivirius. Its free.

AVG will do most of full anti-virus...