Choose best OS architecture, which is better x86 or x64?

Hi,

I want to deliver virtual desktop to office workers and I have limitation on resources, memory and CPU.

I need to advise about OS architecture, which has better performance on x64 processor and ESXi 5.1? x86 and x64 (Windows 7 SP1)?

As you know, x86 of Windows 7 needs to lower resources and it has more compatibility.

Overall performance is impotant for me same as use lower resources.

Thanks