Buy New. Personally I don't think it's worth buying used without a warranty. One leak or crack in the hull in the wrong location can be costly. Whereas with new your covered under Hobie's excellent service.
BUT, if you know what to look for in the model (great source here to search out all the ins and outs) your after, then with some sweetners thrown in and half off a new model, it could be worth it. Otherwise go for all the latest updates/ full warranty if your paying 70 percent or higher of a new model.