[ajessup]

Can definitely advocate Objectify. It's much nicer to work with and if you're working with Google Web Toolkit it is also GWT-serializable, so you can use the same objects in your DAOs and GWT UI.

[Cafesolo]

Agreed.

At this point, I think using JDO on App Engine only makes sense if you're porting an existing JDO application to App Engine.

If you're starting from scratch, Objectify is the way to go.