EF6 is still the recommended ORM and amazing at what it does. EF7 is still missing major features like Lazy-Loading so while you can use it in production, the team has repeatedly said that it's not recommended or necessary unless you have a specific reason to use it. Summer 2016 is when EF7 is supposed to be at full release.

EntityFramework can also support any underlying database and EF6 has providers for sql server, mysql, postgre, oracle, sqlite and many others. EF7 will even support nosql options like MongoDB.

What exactly is the issue with disk space for a published running app? The GAC (global assembly cache) in Windows was originally designed just for this: to share references and avoid having multiple copies of the same binaries. All this led to was a complicated situation with maintenance and reference nightmares. Disk space is exceedingly cheap and a strange to worry about when picking a tech stack.