This is just based on what I have seen and heard. I have only driven a 12R5 for a few laps and never a BMI.

The BMI kicks butt on asphalt. Also a very good carpet car but may have to play with set-up to get it right.

12R5 is good on both but IMO, 12L4 is the way to go on carpet. A lot of people say link cars are quicker on carpet but I have found T-plate cars to be quicker. Of course if you are going lipo, might as well get a link car.