mk 1 rabbits have 2 doors/4 doors and convertibles (cabrio). 78-79 are good starting points.
gas models and diesel models are all 4 cylinder. Diesels will give 45-50 mpg.
GTI models are more power and style.
gas model fuel injection can be difficult to get running right and problematic.
Look for something that has been taken care of and not run into the ground. Be patient and look at a ton of cars so you get experience in what is a decent find.
Look for an interior that is not ratted out and beware, beware of rust in the quarter panels (behind the wheels), strut towers (under the hood), around the glass. Get on vw vortex and look at a ton of cars
I included a link to mine to get you started
VWvortex Forums: yellow 79 wabbit