OE will be quietest, and are of high quality. That is OE, not OEM, which gets confused as OE sometimes. There are many different pad compositions, and one manufacturer can make several different pads, so the safest is to use OE.

OE means in a BMW box, where ever you buy it from. (Unless it is a counterfeit part, which can happen, if you are dealing with smaller or unknown vendors)
OEM means from a supplier that also makes parts for BMW, but the ones you buy are not necessarily the same as the ones in the BMW box. Good examples are filters and oil.
Aftermarket means that it is designed to fit physically, and the performance characters may be similar, or not at all similar.

Only downside to OE is the dust.

If they were sold as being a match to your vehicle, odds are the only thing that matches is the physical size. Very unlikely that they are the OE pad compound.

There are some good aftermarket pads, and some OK aftermarket pads, and some bad ones, simply because they are primarily sold based on a price point.

When you say 'seller' I think of ebay and similar sites, which are full of junk parts.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue