Hi M.
You're right, there's not that much material out there.
So to answer your question, I (quickly) written a blog entry comparing SDO with
EJB 3 (which largely based Hibernate ORM because they seem to have ignored the lessons learned with JDO, so it should answer your question).
http://www.codefutures.com/weblog/corporate/archives/2006/05/sdo_versus_ejb_3.html It's really a chalk and cheese comparison. ORM technologies are for
Java developers that don't/can't/won't like to deal with relational databases.
SDO is really just a simply XML API for accesses
Both are data persistence technologies, but that's about all they have in common.
I hope this helps.
You might also find this comparison of SDO and DAO to be useful:
http://www.codefutures.com/weblog/andygrove/archives/2006/03/sdo_versus_dao.html For other data persistence technology comparisons, you can look here
DAO versus ORM
http://www.codefutures.com/weblog/andygrove/archives/2005/02/data_access_obj.html JDBC DAO versus SDO versus EJB CMP
http://www.codefutures.com/weblog/corporate/archives/2005/02/data_persistenc.html I think the general answer is that it is impossible to say that one particular data persistence technology is 'the best' and that the appropriate choice depends on your particular requirements.