I have play around with both cloud providers. I actually just finish taken a AWS class on last week. If your going to migrate a sql server database to the cloud definitely go with Microsoft. RDS/EC2 is lacking big time in the tools and options. If your force to go the Amazon route go with EC2. That way you will still have some control over your sql server environment. RDS is for people who don't really want do any administration. Make sure you read the SLA. IMO