I admit I don't have a lot of experience with MongoDB, but RethinkDB was really easy to plug into Node. While we didn't support PHP officially, the PHP RethinkDB driver was maintained by RethinkDB's engineering manager, Daniel Mewes, and it looked pretty solid.

When I started at RethinkDB, it was before changefeeds were a thing. I always thought the "killer feature" was, well, ReQL. It had the qualities of an ORM/DB Builder in your native language of choice. There was a poster on the wall that said "Databases should be indistinguishable from magic"; I always thought that was a perfect pitch to the RethinkDB audience. I understand why they canted toward pitching the realtime aspects first and foremost after changefeeds came about, but I thought it had great power even if you weren't focused on realtime/event-driven aspects, and perhaps that should have been emphasized more.