The Jetta is a nice car built on the Gold platform. It is however a diffent class to the mondeo
Jetta more in line with the Focus saloon as mebntioned before, and mondeo with the Passat which is a quality car.
I suspect you have picked out the Jetta and Mondeo because of budget- Your choice depends very much on your needs for space and use. If space is not as much of an issue, meaning 5 adults in the back seat (as you are considering the Jetta) and if you like the fords, a higher spec Focus cdti might come into consideration or a volvo s40 (same car really as focus).
(Personally for that budget I'd get a Golf 2L TDI sport or the Passat)