What's the difference between Spring Data MongoDB and Hibernate OGM for MongoDB?

I have not used Spring Data before but I've used Hibernate ORM a number of times for MySQL based application. I just don't understand which framework to choose between the two for a MongoDB based application.

I've tried searching for the answer but I can't find the answer which does a comparison between the two in a production environment. Has anyone found problems working with these two frameworks with MongoDB ?

Disclaimer: I am the lead of the Spring Data project, so I'll mostly cover the Spring Data side of things here:

I think the core distinction between the two projects is that the Hibernate OGM team chose to center their efforts around the JPA while the Spring Data team explicitly did not. The reasons are as follows:

• JPA is an inherently relational API. The first two sentences of the spec state, that it's an API for object-relational mapping. This is also embodied in core themes of the API: it talks about tables, columns, joins, transactions. Concepts that are not necessarily transferable into the NoSQL world.
• You usually choose a NoSQL store because of its special traits (e.g. geospatial queries on MongoDB, being able to execute graph traversals for Neo4j). None of them are (and will be) available in JPA, hence you'll need to provide proprietary extensions anyway.
• Even worse, JPA features concepts that will simply guide users into wrong directions if they assume them to work on a NoSQL store like they were defined in JPA: how should a transaction rollback be implemented reasonably on top of a MongoDB?

So with Spring Data, we chose to rather provide a consistent programming model for the supported stores but not try to force everything into a single over-abstracting API: you get the well-known template implementations, you get the repository abstraction, which works identical for all stores but lets you leverage store-specific features and concepts.