How to compare ? In Shopping the Cloud: Performance Benchmarks I listed a number of services and reports that compare cloud provider performance results, but the truth is that in computing (cloud included) you can throw money at almost any performance and scale problem.
It doesn't make any sense, therefore, to talk about performance alone, you want to compare price/performance. But here's the rub: it is becoming increasingly difficult to compare the pricing of the various cloud providers. About a year and a half ago I wrote What Are Amazon EC2 Compute Units? In which I raised the issue of how difficult it is to know what it is you are actually getting for what you are paying in the cloud. Other vendors use their own terminology, such as Heroku's Dynos. CloudCmp. Nov. 2010. Hourly Cost. 30 Oct After receiving feedback from several readers and the desire to see the results, I have updated and reformatted my previous Cloud Cost Comparison.
I have included comparisons between Microsoft Windows Azure, Amazon EC2, Rackspace Cloud Servers, and Joyent SmartMachines in this spreadsheet. Cedexis.com.