if you get a 128, get manual + any sport package.
both are definately worth it and will make driving so much better. With sport package you get better suspension, seats, and bigger tires, and higher speed limiter. Manual on 128i is a blast. The auto on a 128i is nothing like the DSG on the GTI.
also, in terms of driving, the gti and 128i are similar but the 128i is RWD so you get a lil better grip and easier to slide