My best experience was with Beyerdynamics. I always liked their headphones better than Sennheiser, although the latter was always rated higher by the audio press. So I bought a pair of their DT 811 headphones 8 years ago and recently the plastic suspension system broke. I sent them a letter and asked them to send me a replacement at my own cost, but they sent the replacement for no charge! They have also been very helpful with servicing microphones I have bought from them.
Best and Worst customer service?
My vote goes for Sonic Frontiers, as Best! I was contacted within an hours, after e-mailing a question. Wery friendly and helpfull!(they can count me-in on the next purchase) Thw Worst? Linn audio! It's been over a month since i submited a Q! I am stll e-mailing the question...i am sort of amused by now!