Personally I would say you are better defining what you want to do and then looking at what each provider can offer to suit your requirements.
For example even just within AWS you can have a SQL Server running within an EC2 instance, this is essentially a full blown SQL Server install within a virtual machine. Depending on the functionality you require you can have the free version which is the windows OS and SQL Server 2008 R2 Express, Or the considerably more expensive versions with Standard \ Enterprise edition.
Or you can have a SQL Server Instance defined within RDS which offers limited functionality, but very little over head for maintenance.
An EC2 server can be shutdown thus not incurring any costs while inactive, but a RDS instance is chargeable by hour and cannot be shutdown.
I haven't look at other cloud providers but I suspect that its not going to be that easy to compare like for like.
MCITP SQL 2005, MCSA SQL 2012