My personal reccomendation would also to go for a BX (though I've had little trouble using the VIA P3 chipsets myself...not that I used them very much) with 4 DIMM slots and as many ISA as you can get.
Also try not to get a non-standard ATX board.
And about the chipsets, it basically comes down to this:
BX usually means stable performance, easy to set up and often come with tons of ISA and DIMM slots but no official 133fsb, no AGP 8x cards support, ATA-33 only and only low density SDR (256MB with 16 chips and no fewer!) will work with it correctly.
Also 100fsb Coppermines are much less common and not all BX boards support Coppermine
VIA P3 usually means official 133fsb, AGP 4x slot, usually ATA-66, supports high density SDR DIMM's but requires a bit more work to set up correctly.
The best advantage would be that you can basically plug any CPU in the board and it will work.
Also I noticed VIA chipsets are a bit slower then BX when using the same hardware.
In the end it comes down to doing a little research before putting the bugger together 😉
And it may also depend on how much spare parts you have kicking around.
If you have basically nothing to start with you may have a harder time trying to get it all to work. If you have 1 of everything and 1 part doesn't work, it'll be much harder to determine what part is broken.
What OS are you going to be using?
Anyway, good luck 😉