I have owned Audis for years. TTRS is a great car and an absolutely phenomenal modding platform. You will be able to get close to 500hp and 500lb-ft in a car that has AWD and weighs like 3300 lbs. Just don't love the looks. Not bad, by any means, but not sleek and sexy like the M3. Good choice. Hope you enjoy it.
It is intesreting how nit-picky people get when comparing BMW M, Audi RS, and Mercedes AMG. These all relatively equal cars, with each having their pros and cons. Can't really go wrong wih any of them.
Audi S6 * Audi S3 * Porsche Cayman GTS
--Former BMW M3 owner