Well certainly for how much you pay and the perf you recieve the SktA AthlonXP are easily king. All TbredB and Barton are excellent o/c'ers often averaging 2.2ghz 400FSB which is roughly XP3000+ and XP3200+ speed ... not bad from CPUs set at XP1700+ and XP2500+ at stock! Barton is roughly 5% faster clock for clock, that's the only real diff. Of course this is if you don't mind o/c'ing but even then the SktA route is far cheaper. Best SktA mobos are based on the nForce2 ultra400 chipset and have Soundstorm audio but other nForce2 are still very close behind as are KT600 based mobos, these all handle 400FSB and should allow a whole range of multipliers and FSB options for you to work with. All you need to run AthlonXP optimally is DDR400-PC3200 which is now a certified spec and pretty darn cheap ... again great for making big savings. The downside is that SktA is nearing the end of it's life and XP3200+ is about as much as we're likely to get ... still with the way Intel change mobo sockets and archies you may find they offer little long term appeal too! In SktA mobo chipsets it makes most sense to go with 400FSB capable mobos, SiS748 are great if you don't want to o/c much otherwise it's between KT600 and nForce2 and the nF2 do have the edge esp with Dual Channel (original and ultra400) and the lovelly nVidia audio chip.
If you go P4 you really do want an 800FSB CPU which all come with HT enabled to make Windows tasks much smoother. Plus they o/c well but still have blistering perf at stock, they'll knock youa fair bit though esp for a mobo to match. O/c'ing is certainly more difficult thanks partly to Intel's locked multipliers and partly to the RAM needed for sync'ed speeds above 400FSB. Synced is ideal but perf is hardly poor when running async. Regarding mobo chipsets Intel 865PE is top choice esp if you can find one with the 875 optimisations built in. It's the mobo, RAM and CPU which will really knock you when going with Intel and it should equate to a small perf gain over AMD for a good 200-300 notes more. Those notes could be put to getting more RAM, bigger/better HD, screen(s) or most importantly the gfx card if gaming is your thing.
There is no bad choice and they have their pros and cons but AMD easily offer better 'bang for buck'.