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Any tips for quality or best value aftermarket ones?
I've had success with Clarks, which are usually significantly cheaper than the OE Shimano ones.
some people say you need to match pads with rotors manufacturers as much as possible, is that a thing?
Not really, bicycle brakes are low tech and low performance. Nobody is actually getting any marginal gains by tweaking rotor composition, because they are buying their rotor material from commodity steel stockholders, not custom mills.
Do you want somebody to address the root question, or your inability to find the answer?
The answer to the former is "whatevs", there are pros and cons to the main options (sintered or resin bonded) which you'll have to decide for yourself. OE Shimano pads are fine unless you think they aren't, in which case good quality aftermarket pads are what you need.
The answer to the latter is that I don't think the question has been addressed before, so there is nothing to find.