Nosedive
White Christmas
USS Callister
Shut Up And Dance
The Entire History Of You
I think PROBABLY in that order
. (edit: I actually changed my mind, haha)
I also really enjoy Metalhead - although it's generally one of the lowest-rated episodes. I think it did a great job of building atmosphere. And Smithereens is a great hour of television, just extremely well made and acted, though it doesn't necessarily feel like a Black Mirror episode...? As a short TV movie it's excellent.