SearchServerVirtualization published a nice article providing some suggestions for choosing between Linux and Windows as host OS for VMware Server.
It’s just a big short and the analysis could be much more complex, involving aspects as easiness in virtual machines files backup strategy or in performances optimization strategies, but it’s a good beginning.
Read it at source.
Meanwhile many (including me) are waiting VMware will support Sun Solaris 10 as host OS as well. At that point a deep comparison will be even more interesting.