If you take overclocking into account, the AMD hands down every time.
I just recently found myself in this situation. I pined for about a month over if I should get Sandy Bridge 2500k, or an AMD quad. The Sandy bridge chip is $225, and the cheapest mobo I could find to suite my needs (limited supply right now...) was $179.
I decided on the AMD chip (955be) for $100 less, and the mobo for that platform was another $100 less. With the savings, I was able to pick up a radeon 6950.
If budget isn't an issue, of course, I would go for the 2500k every time. But for the money I had to spend, I got WAY WAY WAY more for my money by getting a 955 BE.