Multitude of tools / frameworks - key differentiators?

[Tina Coleman]

Object-relational mapping frameworks seem to be cropping up all over the place. I'm aware of Torque (actually seen it in use in the Scarab bug tracking database), Cayenne ( http://www.objectstyle.org/cayenne/index.html), OJB ( http://db.apache.org/ojb/), and Hibernate ( http://www.hibernate.org/). Then there's JDO, of course, which tackles the same basic problem (object-relational mismatch) from a different perspective. What are some of the differentiators folks use to make a decision amongst the toolsets out there?