It all depends on the part and what kind of car. O2 sensors, thermostats, spark plugs, and motor mounts I only use OEM. Anything else I'll use decent aftermarket parts.
I used 2 A1 Cardone reman power steering pumps that were trash for my Jeep, ended up getting a ridiculously priced one from the dealer. The Jeep has Raybestos rotors, Bosch brake pads, Timken wheel bearings, Monroe shocks, Moog control arms and track bar, etc. All work great and I didn't completely empty my wallet on dealer parts for those.