SQL or NoSQL

What kind of database? We would like to be able to deploy in the cloud or on the client site, so we don't want to have a big database requirement. Something that we can install locally for no cost.

Candidates could be

Relational

• SQL 2012 express
• SQL Lite
• MySQL
• SQL Azure (Always store in the cloud)

NoSql Document Database

• CouchBase
• MongoDB
• RavenDB
• DocumentDB (Cloud only)