Anyone help an old guy here?

Basically I want to buy an xbox kinect bundle for fitness. My wife is interested in the dance stuff. I like the look of the nike trainer.

However I'm confused with all the variants.

I see some consoles say 4Gb, and some say 250Gb..and are they all HiDef?

Can anyone advise me please? It's not really about the money I just want the most appropriate. If it's any help I'm probably not interested in online gaming. Just getting the heart rate up and de-stressing occasionally.