I am in dilemma to know which is the best graphic card between ATI and G- FORCE and about to buy a new graphic and I can invest so much money for graphic purpose.Kindly please tell me which is best card for gaming applications and rendering purpose and even tell me which is the best for video output and video input in the world at present.

I am totally confused to identify which is the best between these two.

Best is certainly a relative term.
WOrth seriously considering would be an nVidia SLI Card (http://www.slizone.com/page/slizone_learn.html), basically this is TWO cards that act as one but produce, what is thought to be, the Ultimate in gaming.

Yeah but ati has crossfire now... anyway I'm an nvidia guy myself due to the easy oc'in but at stock speeds both companies will go back and forth for the best atm card the same as the world of cpu (amd v intel) and if you really want to spend around 1700 at least to have the best in gaming experience (thats just for the 2 cards and sli/cf mobo I'm guessing your going to need) and if you do buy go big or go home get the new intel (another 1000 iono exact price to rich for my blood ) and 2 gigs of ddr 400 and I'm sure your going to want a xfi sound card another 280 I think (check newegg its been awhile) and then that's basically the only set up ull need to have the best cards atm because just have the best grphx card is useless without the rest of it