What cloud computing environments have you used (CloudStack, OpenStack, OpenNebula, Eucalyptus, Amazon EC2, AWS, Google App Engine, Salesforce, Microsoft Azure ...)?
The answer depends on the purpose. if you are looking at a public cloud deployments for factory type app deployments, i like AWS, but if it involves others things like hybrid capability, customization and stuff like that, prefer OpenStack
I am using OpenStack cloud for my real life work and research activities. I find OpenStack as highly scalable and elastic. Previously I had experience with Eucalyptus. I strongly agree with Mr. Robson Lelles that cloud users should not feel that they are using it. For more information,I have numerous publications in this field that you can take a look.