This is a fun one! I tested out a RS5 before re-upping in the M3. RS5 was a nice car, and it's a high revving and powerful as well. I just didn't like the seating position, the mass of the car (not literal perhaps, but the feeling it was a "big" car), and the way it was geared. If I was a suit who wanted a nice GT car that was exclusive, it would be the ticket.
For my purposes (track fun, modding, cost / options to do both, etc.), the M3 just made more sense for me. Reviews are too subjective to each editorial team. Like everyone has said, try both out and find out for yourself.
Good luck, and what a fun problem to have!
Last edited by S65NAPWR; 11-22-2012 at 08:39 PM.