I'd like to understand why 3 totally different databases are in your final list of possible choices.
We are also looking for a proper DBMS and the first choice was between SQL or NoSQL. We need very flexible schema, so NoSQL is the direction we took and started looking at CouchDB and MongoDB. MongoDB winning our hearts. After some time and contemplation and a little bit of development, we decided we can't do what we want to do smartly without the database supporting relations. We could have done it on the application side, but that just adds a ton of unnecessary complication. So, we had to go shopping again. Now we are looking at TitanDB and OrientDB, and we are tending more towards OrientDB.