If you're going for a gaming machine, AMD does really well. I run an AMD 8150 (8 Core AMD 3.6Ghz) on my gaming computer and it just screams. Add in the Solid State drives, the cooling system etc, and it's a beast of a machine. While an i7 will outperform it, I haven't had any issues at all as of yet.
From a server level however, I'd still go with Intel. Intel Xeon's has the server world locked up. The Xeon is just built for servers and does an amazing job of running 24x7 without issues. A single i7 can compete pretty well with a reduced clock speed of an 8 core Xeon, but when you combine the ECC Memory and everything else that goes with it, a server that requires multi-threaded performance will do wonders.
I guess you need to evaluate if you're running a system that requires highly threaded performance or lightly threaded performance. This will depend on the software being used. For me, if I require high performance, there's limited that stops me from reaching for the Xeon.
We use some Xeon E5's with 32GB of memory for our eCommerce servers and while that's not the same as Gaming, the performace and demand can be similar at times. We love them.