I asked this question not too long ago and this is what I was able to decypher...
AMD has a slower car, but a shorter racetrack to travel. Pentium boasts about their fast car but doesn't mention that they have a much longer road to travel.
AMD is cheaper but tends to heat up a bit more and be a little more unstable than P4, and that is where the money goes (if you don't include the fact that you're buying the name).
I have narrowed it down to this...it's an apples and oranges thing. There is no clear answer to which is necessarily "better." So my logic is, if you can't conclusively prove one better than the other, its so close that it's not something to worry about, so just go for the cheaper one...AMD.