
Putting personal preference and opinions aside, both are very fine and capable CPUs. P4 do tend to offer cheaper and less problematic mobos though. P4s do run much cooler and o/c much better.

Speed-wise, an AthlonXP2000+ will equal a P4 256k 2.0ghz 400FSB (ie Williamette) in apps, and equal a P4 256k 2.2ghz 400FSB in games. However big factors for me are, firstly that any of the new 0.13mu P4 512k CPUs (ie Northwood) will easily attain a 533FSB with stock cooling and no voltage increase giving the 400FSB NW CPUs (P4A) a huge boost in both perf and speed (eg P4A 1.8ghz 400FSB o/c easily to 2.4ghz 533FSB). The AthlonXP2000+, 2100+ and 2200+ however DON'T o/c at all, they simply run far to hot at default settings! If o/c is in any way a factor definitely go P4. Secondly P4s have recently changed to Skt478 which looks to have a much longer life, whereas SktA has been around since 600mhz CPUs and seems to be showing its age and its bottlenecks. With even the new 0.13mu T.bred AthlonXP2200+ running way too hot (it looks problematic for AMD to even release a XP2400+) it seems the SktA days are numbered, esp if I hear correctly that AMD have already developed a new Skt archy. With a Skt478 mobo you are pretty much guaranteed a cheap and easy CPU upgrade in the future whereas SktA CPUs are much more likely to be both rare and pricey in 12 months time (Just like original Athlons using a 200FSB are now, and a lot of people have SktA mobos which can't use a 266FSB).

IMHO. If you want a very fast CPU, both AthlonXP and P4 deliver. If you aren't concerned about o/c then the AthlonXP makes more sense unless you plan to add a faster CPU in the future then the P4 Skt478 would be better. However don't consider running a NW P4A at 533FSB as o/c, it is of course, but it is more like running the CPU at its capable speed than actually surpassing it. In the same way as running a GF4TI4200 128MB at 250/500 isn't really o/c, like the GF3TI200 it is intentionally clocked lower in order to promote sales of the higher priced products above it! Oh and there's no need at all to couple a P4 with RAMBUS (PC800 or PC1066) as DDR333 works incredibly well with P4s unlike AthlonXPs.

Anyway here's a couple of benchmarks to show the diff in 3Dmark2001 with a GF4TI4200 (CPU, marks, games high detail FPS):
1024x768x32:
Athlon XP2000+: 10000, 53, 107, 65, 46
Pentium4 2.0ghz: 9000, 48, 90, 60, 38
Pentium4 2.5ghz: 11000, 63, 110, 78, 47
1024x768x32xAA:
Athlon XP2000+: 8000, 49, 81, 57, 39
Pentium4 2.0ghz: 7000, 40, 73, 52, 27
Pentium4 2.5ghz: 9000, 58, 85, 64, 35

I've included a P4 2.5ghz to give you an idea of what the P4 2.0ghz should easily obtain when o/c. In all cases I have used the average submitted result as opposed to the top result where possible due to this being more accurate in showing obtainable perf. Obviously different games will give different results but this does give a good indication of each CPUs capability.