AMD vs. Intel-
Both are about the same quality.
Intel has slightly better compatibility, but nothing you can't work around if you try.
AMD is cheaper. A lot cheaper.
The sum of my reasearch lies before you. 
I'm using AMD and have had no problems so far.
If this were 2001 I would completey agree with you. This is no longer the case.
Intel has drastically better compatability as it pertains to mame in particular. The mame devs reccomend intel processors if you are trying to run any of the high-end games. Benchmarks show that you'll get a 10-35% preformance boost because any and all 64bit/multi core optimizations in mame's compile don't even apply to a similar speed AMD. It isn't a matter of one brand being better than the other, but rather the devs use intel, so you should as well.
AMD isn't drastically cheaper anymore. They used to be, but this just isn't as true as it was back in the day. The thing you need to understand though is a 2.4 ghz quad AMD is NOT the same speed as a 2.4ghz quad intel. You need a 2.6-2.8 ghz amd to have comparable specs. If you understand that and start pricing the price difference is very slight.
Let's put it this way... I've alwyas been a hardcore amd fan. I've always bought amd processors for my pcs and mame cabs. Last year when I upgraded my desktop I finally realized that the intel processor was going to cost about the same... so I took the plunge. One year later and I don't think I would put a amd processor in a cab unless it was a used pc and the cab wasn't going to run high-end games.
Btw I don't necessarily disagree with your assessment if you don't really care about the horsepower of the machine and just want a basic mame setup that plays the games of the 80's and 90's. I just meant if we are talking high-end here.
Just for the record on the other debate... I love to play games... BUT I've had a mame cab for over 14 years. (Damn I'm getting too old for this -----) As huge as that library looks, at some point you DO play it all.... or at least all you would be interested in. I've got to really dig to find something that I enjoy that I haven't played to death at this point.
I love tinkering with the cab though, especially the software. But then again I have that near fatal disability of being a programmer.
