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 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 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...