Using MS Sql Server 2012 free with dbGo (migrated from Ms Access), for more than 8 years with great success for small companies (for accounting and medical software). Not a single file corrupted!
Scale perfect from LocalDB - monousers (with automatic installer), to Express edition for remote, but no experience with cloud now. Simple to install and maintain.
Worked with success in the past also with Firebird, but they don't have automatic management of versions installed and instances for server like MS Sql Server.
In case of migration to .net, the support is exceptional with linq, entity framework, dapper.