Which is better in virtualization?Vsphere or Hyper-v?

Both, are very good Hypervisors, e.g. VMware vSphere and Microsoft Hyper-V, it really depends on your requirements, and if you have any experience of either technologies, as to which you implement.

There is also Citrix Xen to consider as well.

Could you give me more background, as to what hardware you have, will you be purchasing hardware, e.g. servers and storage (SAN or NAS).

Thanks  for your support
-@ Andrew Hancock
What do you mean by "There is also Citrix Xen to consider as well."To consider what exactly?

Consider it as a solution.  There are more than two products that provide virtualization on the market.

Mr. Leew
For my knowledge Citrix Xen is to publish applications? The concept is different than vsphere and hyper-v

Citrix Xen Server is a Hypervisor!

see here

http://www.citrix.com/products/xenserver/overview.html

You are confusing Xen Server with XenDesktop and XenApp!

My IT environment is :
-exchange server 2010
-2 Windows 2008 server as domain controller
-Web server (Windows 2008)
-Archive server (Windows 2008)-
-Sharing Server
Currently I don't have NAS or SAN

you can use FREENAS if you are very restricted in budget

I'm actually doing just that in my home lab. FreeNAS works pretty decently as a low-end NFS datastore for VMWare.

But I would NEVER, EVER put that into a production environment for one of my clients. I just don't trust it.