CloudSleuth's comparison of 13 cloud services showed a tight race among Microsoft, Google App Engine, GoGrid, Amazon EC2, and Rackspace.
http://www.informationweek.com/news/cloud-computing/infrastructure/showArticle.jhtml?articleID=229300184
Top 15 Cloud Service Providers – Ranked by Global Performance
https://www.cloudsleuth.net/web/guest/blogs/-/blogs/122498
