What is the best operating system for accessing cloud-based services? Windows? Mac? Linux? gOS?

In my experience, the best operating system for the cloud is not an OS at all. It's Express Gate from ASUS.

This BIOS managed application boots up in 5 seconds and has a fantastic built-in web browser that works great with Google Apps, Salesforce, and many other applications.

Even though the actor in the video below is using a desktop, this would make an ideal Netbook OS.