I am a AMD person and just looking at the description of the two cpu's I see this.
Intel Core i7-2600 Sandy Bridge 3.4GHz (3.8GHz Turbo Boost) 4 x 256KB L2 Cache 8MB L3 Cache LGA 1155 95W
AMD Phenom II X4 975 Black Edition Deneb 3.6GHz 4 x 512KB L2 Cache 6MB L3 Cache Socket AM3 125W Quad-Core
Native the AMD is faster but the Intel uses less wattage.
AMD uses 4 x 512KB L2 Cache 6MB L3 Cache
Intel uses 4 x 256KB L2 Cache 8MB L3 Cache
AMD uses more L2 cache
then the Intel but has less L3
The big difference for me is the price.
AMD is 189.99
Intel is 299.99
Now the opinions of each person will differ and always have been between Intel and AMD but I prefer the AMD for gaming. I would suggest looking at the motherboards and try to find one manufacturer that makes the same board for Intel and AMD. That way you can see the price difference there. The boards will be identical except for which CPU it will accept.
Hopefully this helps a little in your decision.