For one of my projects I prefered using Django+Mongo.
Why should I use MongoEngine, but not just PyMongo? What are adv
I assume you have not read the MongoEngine claim.
MongoEngine is a Document-Object Mapper (think ORM, but for document databases) for working with MongoDB from Python.
This basically say it all.
In addition: your claim that Pymongo would deliver objects is wrong....well in Python everything is an object - even a dict is an object...so you are true but not in the sense of having a custom class defined on the application level.
PyMongo is the low-level driver wrapping the MongoDB API into Python and delivering JSON in and out.
MongoEngine or other layers like MongoKit map your MongoDB-based data to objects similar to native Python database drivers + SQLAlchemy as ORM.