The transmission you describe is more than likely the Audi 016 type box. What you now need to determin is which model of that box you have because each model has different gearing some being better than others.
There is no one answer to your question as to what box is best, is it which is best in the Audi range, 5 or 6 speed, Porsche or ZF. I would suggest that you work with the search option and do some research. You will find that in the mountain of information contained on the site is insite to all of your questions. I say insight because so much is involved in determing the correct answer for your requirments that you really have to do the research and understand what is available and what the cost and instalation requirments are for each transmission.
Good luck
Peter