I haven't tried the Jet sharpener, but I had a long talk with one of the tutors at Axminster Power Tools (just up the road, lucky me) about the various merits and demerits of both, and looked not so much at the machines as the construction quality of the tool holding attachments. Although the Tormek attachments were more expensive, they were of much higher build quality imo.
According to the chap at Axminster (I know they're in business but have more than once in the past directed me towards something cheaper, saying it represents better value for money), the Jet designers essentially bought the Tormek system and worked out a way to copy it cheaply. I got the Tormek and have never regretted the choice.