Amazon EC2 wins (Score 5, Informative)

I run a small startup in the Boston area and have been using Amazon EC2 (plus S3, SQS, and the rest of the AWS family) for the last year. It's worked for us like a champ. A little downtime in the beginning plus some S3 outages, but with the right backup, failover, and restore procedures in place we've gotten reasonable uptime.

The big requirements for us were the following:

1. Ability to move our website (and code base) elsewhere if needed. Could be in-house, to another cloud provider, etc.
2. Minimize up-front cost and allow for massive scaling if needed
3. Cost competitive servers/computing over time
4. Cost competitive storage/disk over time

App Engine fails the first criteria, since (at least currently) you can't build a BigTable application on anything but Google App Engine. "Cloud computing" in general beat out traditional hosting on the second, third, and fourth points. I hadn't checked out GoGrid or AppNexus at the time, but other competitors (Sun, etc.) couldn't match Amazon's price-performance specs.

So, with all of those requirements, Amazon EC2 won out and I'm a happy customer.