I have both (X5D and XP30). If you are looking for all around good sounds and greater variety, go for the JV-1010. I would recommend it as well because you can install an additional SR-JV card. In addition to all sounds from the JV-1080 and 2080, you get the Orchestral and Session expansion boards built in (the Session board in my opinion is one of the best along with Vintage Synth).
I bought my XP30 first and then the X5D because I was looking for some signature Korg sounds (M1 Piano, Pick Bass) to broaden my sound pallete.
In defense of the X5DR, you can program sounds from its front panel - the JV-1010 needs to be connected to a PC and the included Sound Diver software must be used. The X5DR also has better sounding EP's much like what the old Yamaha DX7's could do. The XP30's EP's are just too thin.
I agree with the above post. I have previously owned the JV 1010 and the Roland XP 30. I have also used the Korg X5DR extensively in the studio. The Roland module is hands-down the better module. The Korg has a few good patches, but the Roland has a lot more great patches.
If you don't need to get your module right away, you may want to wait for the new Roland module. It looks like a replacement to the JV 1010 soundset. I currently own an XV 3080 and it was well worth the money for the stereo samples and better soundset. The new module includes the same soundset as the XV synths and samplers. You may want to wait for it. Here's a link: http://www.harmony-central.com/Newp/2001/XV-5050.html
