Spec breakdown of jetta models

I am looking into purchasing a used car and i am beginning to consider purchasing a vw but I know nothing about them. I currently have a Pontiac Grand Prix GTP that hauls a*s so I am looking for something with some get-up-and-go but has decent mpg.

I am looking at the Jetta but I was wondering if someone would give me a breakdown and the pros and cons of the Jetta TDI, GLI, VR6 models.