A good friend of mine - E92Fan over at the UK section - has been running the AP BBK for a few years and is very satisfied with it. IIRC he upgraded it with PFC discs and uses track pads when going on a circuit. Another friend of mine uses the same kit and is also very happy with it; generally speaking AP has an excellent reputation in Europe and the UK and is also not the most expensive solution.
StopTech is used among others by Alpina on their B3 GT3, and pursuant to reviews of this car the brakes are quite good (the magazine sport auto tested this extensively it appears).
Personally I'm running a Performance Friction BBK which is IMO the most technically advanced of them (but also among the most expensive) due to its monobloc design and one-pad-per-piston feature.
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