Don't go turning this into a flamefest now people. If you have an opinion, justify it.
Anyways, I will be blunt, the P4 architecture is garbage right now. The only thing Intel has which even keeps them competetive is Hyperthreading which can allows the CPU to use two threads, just not simutaneously. Any Intel without Hyperthreading doesn't stand a chance at competing with an equally priced AMD.
The revised P3 architecture found in the Pentium M right now is impressive though however it still isn't in full swing and probably won't be until next year.
AMD has a real advantage right now with the Athlon 64. The big thing is the intergrated memory controller. Intel still uses the northbridge and thus the FSB still has communicate between the CPU and that. Intel can only increase memory bandwidth by continually increasing memory and FSB speeds.
AMD however, still uses DDR and can achieve the same or greater bandwidth than DDR2 via the hypertransport bus, which is a high bandwidth low latency link directly
between the CPU and RAM, rather than the Intel going from CPU > NB > RAN.
64 bit makes no difference apart from how much memory the core can address.