"which is better?"

That's quite a large candle to light...what are you expecting and what are your intentions for use of the computer...if for media or gaming use I'd definitely go with Intel and specifically the Nvidia graphics. If and office machine either will do nicely.

Upon the release of the i7 the cost was about $1600 though now nearer to $280 of course the new poster-boy i7 extreme is about $1000. The AMD is available at about $180. The basic i7 core Lynnfield and the AMD X6 are about equally matched.

I suggest configuring a system that can take advantage of a processor adequate for your current need and be capable of upgrading to meet unknown future requirements. Get a Motherboard with DDR3 hi-speed memory capability but that will also accept a moderate grade too. Start with this good configurable Motherboard; Gigabyte is my recommendation, and load it with a moderate core i7 processor, reasonable RAM and a good middle of the road stand alone graphic engine, a 700+ watt power supply. Do this which the idea of how it may be upgraded later and continue great service without necessitating a new build.