It depends on how different the M brakes are when compared to the standard 3 series setup.
Personally, I am looking for a 6 front/4 rear setup. My buddy had StopTech brakes on his WRX, and they were very nice, and performance was on par with my JDM Brembos. For the price, they are a great deal.
Alcon, and Endless make some nice brake products as well.
Brembo is always my default choice though.