Hi Punna,
JDO is good. You want to check out the new JDO 2 releases, as these add features like Fetch control and advanced Querying which were previously non-standard.
Sun's JDO-RI is not a real usable JDO implementation, it does not support RDBMS or multi-user requirements. It's more an example and resource for JDO vendors to work from.
JDO 2 is fully comparable with Hibernate, and may have some advantages -- better handling of == operator, standardization, clean separation of model from storage, etc.
Hope this helps.
Cheers,
Thomas
www.powermapjdo.com