I think you're looking for an answer that is maybe a little more subjective than objective. No one seems to have had a bad experience with any of these models, so you probably have to get on the bikes and see how they feel to you. Can you go to a local store and try them out? Even if you're buying used, at least you have an opportunity to feel them out.
I have a Spinner, but it is a higher model than the one you are looking at. Honestly, I couldn't tell you if it has a chain or a belt and didn't realize there was a difference! It works fantastically well and that is all I care about.
I think you need to just go with your gut here. If you don't like it, you can always sell it down the road.
Good luck!