Depends - if you plan on running the higher clocked AMD,s (1.4 or higher), try the most recent official BIOS from Iwill - I believe it's the 0515 version.
I use Luckydaze's 0426 BIOS (RAID version) which is a modified/tweaked version of the official BIOS. My Iwill KK266R runs nicely with this BIOS.
You need to read up on Iwill stuff at the Iwill forum in AMDMB.com. You'll find a bunch of threads (along with download links) discussing the merits of the other BIOS versions. From what I can tell, the preferred BIOS is either the 0307 or 0426 Luckydaze versions.
Good luck.