The nForce mobos are good stable mobos.
They are slower than both the KT266A & KT333, but you're not talking much.
The KT333 is the only SktA mobo to gain perf from a sync operation of 266FSB & 333RAM. SiS runs slower at 266+333 than it does at 266+266! nForce gains nothing from what I hear.
O/C! nForce plain suck at this. VIA KT266A/333 are easily the o/c king. AthlonXP's up to XP2000+ should obtain a 145 (290) FSB. You'll gain the best perf from either 266A or KT333 using DDR333 CL2.5 (PC2700) set at 145FSB and RAM timings of 2-2-2.
nForce has got great quality o/b components. The 5.1 sound easily equals the SB Live family, esp for CPU usage. The LAN/NIC is also very good and allows settings to alter CPU usage depending on how important throughput is to you.
If you're unsure whether you need RAID or not then you don't. Don't pay extra. USB2 is a definite advantage, well worth paying a little more for.
MSI have seemed a bit more miss than hit lately, a shame because they used to be among the best. Abit are quite pricey, but most users say they're worth it!
I would suggest shopping mostly by cost. SktA is looking bleak with the 0.13mu T.bred AthlonXP's both delayed and a huge let down. The Hammer/Opteron should be AMD's saviour but will use a new Skt interface. Heck, the SktA has done fantastic but has been in use from 600mhz CPUs, perhaps showing its age and its bottlenecks a little now. It's a shame that AMD seem unable to make the most of SktA, but a 0.13 CPU that runs VERY hot at 1.8ghz (albeit XP2200+ equiv to a P4 2.2ghz @ 400FSB) and archy that doesn't gain from DDR333 nor 333 synced FSB simply give concern.
With the Skt478 P4A (Northwood 400FSB) being bargains and easily o/c to 2.1ghz on a 533FSB I would certainly consider them. The Skt478 mobos aren't that pricey (SiS650 $50) and now that they can get the best from DDR333 they aren't an expensive option. Most Skt478 mobos also come with ATA133, AGP 8x & USB2 as standard. Just thought it might be a consideration.