OEMs will buy in quality parts put in their own boxes – eg Peugeot use Purflux filters with the Peugeot logo on and in a Peugeot box. Audi normally use Pagid pads which again might be in an Audi box if you get them from the dealer.
When you look at ECP and the like you will see cheapo brand pads and discs and you will see OEM quality ones from brand names. The part codes at ECP indicate if they are OEM quality or just compatible and there is a guide there.
I normally stick Pagid or Mintex (same company now I think) for brakes, especially pads. Filters I also stick to OEM and either buy direct from the dealer to be sure (in the case of oil and diesel) or buy stuff I know is OEM – eg I buy genuine Bosch diesel filters and Purflux oil filters from AEP direct.