It depends on many factors. A new may be right for you, but if you're a good mechanic and don't mind, used may be a better option. Sea-Doo develops exceptional service manuals. Keep in mind, that even if you go with a new ski (with the warranty), that warranty will not typically cover off-season storage preparation.
If you go with used, you'll need to put together a checklist for things to look over on the used ski so you don't overlook any glaring defects. Additionally, you'll want to put the used ski in the water to see how it runs.