Stranger Things. Honestly, I don't love Black Mirror as much as everyone else. I think some episodes are amazing, like 20 Millions Merits, but there are plenty of other episodes I find to be just dull, like Nosedive. Stranger Things is something I can never get bored watching.
Stranger Things 3. Black Mirror is an anthology series which is harder for me to get hyped about. Since ST is a serial, I become more invested in its characters, their development, and the story progression.