I recently reviewed a detailed comparison of the top 5 IaaS cloud providers and it listed Windows Azure as having the best overall value (both in cost and performance).
The interesting thing about the comparison is they used a benchmarking tool called Unixbench running on Ubuntu linux.
The irony of a Linux distribution running better on a Windows cloud platform than Rackspace Openstack which itself uses linux is just too awesome not to highlight and draw attention to!!
The full article is here and I highly recommend it.
The Cloud Technologist 