They both have thier differences with strengths and weaknesses.
AMD has done better with multiple monitors. One card can render three monitors. Nvidia can only run two with one card.
Nvidia has done better with 3D Vision. On a hardware support level and hardware rendering.
Nvidia offers Cuda technology. (Useful in certain applications)
Nvidia offers 2.5GB & 3GB VRAM flavors.
AMD & Nvidia both offer 1GB & 2GB VRAM flavors.Now to debunk some garbage propoganda.
"Nvidia runs hot" - SO? That's not stopped them from competitively performing. After two years they've proved that's a non-issue. GTX 400 series cards are an awesome price/performing card right now. The 500 series are even better now.
"AMD's drivers suck" - REALLY? Though Nvidia has a better history track record, it has driver issues too. Both have them and fix them with follow up drivers.
At the end of the day regardless of which you choose they both can accomplish the job. Each can game very well and do well in different games. They both have competive cards pit against each other that perform on par and very comparable.
I'm sure this thread will get ugly eventually, because what both have is some loyal fan bases. It's actually a good thing one doesn't succeed and monopolize the industry over the other. IF either would be the sole GPU company you can epxect HIGH pricing from the sole survior regardless of who it was. As consumers we got them right where we want them, competing for our money at lower priced offerings and constantly looking to improve.
Now to prepare