We were using GAE, Amazon EC2 (also Elastic Beanstalk), Rackspace, Heroku and Jelastic. So I can share some feedback.
With GAE, it was easy to setup environment. The only drawback is the limited control over certain things related to domains and forwarding etc. That did not allow full functioning of our project technology.
Then we turned to AWS and Rackspace. There we had complete control, but it was very hard to set up things manually. Every time we need to configure the project, it was a total pain, and we had to do more IT tasks than we should.
Now we stopped on Jelastic having control over environments with ease of setup. At first, we were using their public cloud (the choice of hosting providers with prices are stated here https://jelastic.cloud/) but after growth moved to private on premise (license based per server price).