Best setup for Debian,CentOS,FreeBSD,WinSvr2003R2,WinSvr2008R2

Hello,

I run vms with this os: Debian,CentOS,FreeBSD,WinSvr2003R2,WinSvr2008R2
Every VM with KVM but i think i do something wrong becouse i get low performace.
Anyone can help me what is the "best" setup for this os's?
I "want to know":
HDD Bus type
HDD Format
HDD Cache
CPU Type
Memory (fix size or auto)
Network model

Thank you!

(Sorry for my bad english.)