Getting started with Heroku is very easy. It's a very straightforward procedure and a beginner can set up their first app in two minutes. Often it's just a matter of a couple of git commands and it's all set up and running. The official Heroku docmentation also helps a lot.
Heroku has a vast list of plugins and services that can be added to an instance. These plugins cover things from databases to email systems. This remove the task of having to install services and setting them up manually. Heroku does it all for you.
Heroku instances can easily be scaled up or down by increasing or decreasing the number of available dynos for that instance. This can be done through the CLI or through Heroku's web UI.
When your deploy fails you see a legitimate error log. Many of the other PaaS give you nondescript messages and debugging is a pain. Debugging Heroku wins by comparison.
Heroku is one of the oldest PaaS providers. The fact that it's been around for such a long time means that it had a lot of time to mature over the years. There's also a massive number of articles, guides and tutorials on Heroku out there for beginners and advanced users.
If you want to fully customize your production environment, then Heroku can be seriously constraining. Installing libraries or services can not be done unless there is already a Heroku plugin for it.
While starting with Heroku is fast and easy, and the first few deployments are actually very fast, larger applications tend to have slower deployments. It takes some time for the dynos to restart and while they are restarting the application is completely offline. Which means that you can lose precious seconds of application time.
Heroku starts getting really expensive once you leave that free tier. It's not just the bare Heroku service that is costly, the addons as well are very pricey.
Clever cloud automatically scales to the developers needs. It auto-scales up when traffic is increasing and scales down to save money when traffic decreases.
The customer support at Clever Cloud is amazing, they will reply to emails, tweets or even phone calls in a timely manner to solve every problem a customer may have.
Getting started with AppHarbor is pretty easy and straightforward. You sign up and after a few clicks you choose the database system you need and you are ready to deploy your app.