I'm looking for a 4TB External HDD. What brands or models are currently recommended? What subpar brands or models should I avoid and ignore? Seagate and WESTERN Digital seem to be the BIG brands but what's the difference? Thank you.I suggest a My Passport Ultra from WD

It's a standard format drive not SMR (Shingled MAGNETIC recording)  https://en.wikipedia.org/wiki/Shingled_magnetic_recording
Powers down when not in use, parking the heads off the platers.
Western Digital designs the circuit board and Firmware  for USB operation. Other manufactures use standard 2.5" drives with a SATA to USB interface often using a drive which needs more current to start than the USB port can deliver.
Hi

SEEMS you have brought an SMR format drive, if it is the model with the black textured case make sure you don't rely on it as the only copy of your files. You shouldn't rely on 1 copy anyway.
I disagree about you comment that pen drives are not reliable. I have expensive pen drives which are 18 years old which are still working daily. Like most things you get the quality you PAY for.