IMO, if you are turning only pens and other small items either will do it. If you plan on turning larger items, such as bowls, the Jet is a better choice because it has a slightly bigger motor and can go slower for out of balance pieces. I believe the jet also has more distance between centers for longer spindles.
As Bill said, it depends on what you will be turning. If only pens and small spindles you can save money by getting the Comet II.