ESXi is a headless server product, not for the desktop…
We have a few boxes here with it on, running VM XP desktops for people to Remote Desktop onto.
All depends on what you want from your workstation…..
Either Win7 x64 as the host, with VMWare Workstation 9 on top – or Redhat/Debian/Slackware/Whatever as the host, and Workstation 9 on top…
Do you work on “one or the other” during the whole development project – if so, dual-booting might be an idea (reboot to other OS when a project requires it…).
There’s a big difference between server (Xen, Hyper-V, ESX) and desktop (Worksation, VirtualPC, VirtualBox, Qemu) virtual environments…