Main differences between the different versions of Linux:
<2.4 old, deprecated, poorly supported (if at all) at this point, stable, but don't bother
2.4 better SMP support, better networking, IPTables instead of IPChains, stable, good hardware support, probably your best bet.
2.5 development version, probably cleaning up a bunch of stuff and whatnot, probably not up to par on the stability side, don't use it unless you have something to contribute.
I'm not sure why so many people keep listing distributions though...