I have limited experience with the Seattle service reps for my M3 in since I only went there for the 1200 service. I dealt with Marc Mercier at Bellevue and have nothing bad to say. Service was done on time and accurately.
I have also heard good things from Alex Long at BMW Seattle.
Hope that helps.
Current: 2016 F80 M3 SO | AB XT1 | ZCP | etc.
Previous: 2009 E90 M3