This is one of the biggest toss-ups in computers. Both have their pro's and con's but here's my take on it.
AMD's-Yes they may run faster at lower clock speeds, but if they run hotter, wouldn't this mean that AMD is overclocking their chips a bit and then advertising them as lower clock speeds? just my thoughts. In terms of average computer user machine's, I think that the P4 is better because the average user doesn't want to take extreme measures the cool their PC.
P4's-Currently I do run a P4, but I do not think P4's are the best. The one thing I do like about them is that I have had any major performance drops. My P4 has run at or above it's listed clock-speed the entire time I'ved owned it. In terms of bus speeds, the current 2.53 ghz P4's have a 533mhz FSB, and these P4's are being listed as the latest and fastest, so AMD is maybe sloutching a bit on releasing a faster Athlon XP. P4's also run cooler, meaning less worry of system freezes or lockups, or fried chips.
Personally I don't favor either more heavily than the other. I would take a top of the line machine with either processor. I don't believe any of the "runs 50% faster at a lower clockspeed..." or any of that-It's all advertising, and without overclocking there is no physical way a processor can run faster than it's internal clockspeed. I will stick with judging by the clock speed, as nowadays any processor over 1.3 ghz is about the same AKA you don't notice a big difference.
Just my thoughts