For a very extensive comparison between seemingly all the O/R mapping tools known to mankind check this wiki page.
Perhaps a relevant observation: despite the zealoting, Toplink, OJB and Hibernate (by far _the_ most popular ORM-tool, and the basis for EJB3) all seem to offer roughly the same functionality. And actually, the XML configfiles also don’t look all that different to me either..
Some notable differences/facts:
- Hibernate has a big following, development continues at a rapid pace. Free, OS, but no GUI except for some crude 3rd party tool
- OJB has a JDO implementation, the other two have not (for what it’s worth, since the JDO movement seems to be running out of steam). Also OS and free as in beer. GUI under development.
- Toplink doesn’t support MySQL, PostgreSQL or SAP-DB like the other two. It does have a pricetag but also a nice GUI