Luke Cage is my favourite, and most anticipated solo. I wouldn't say it was the best season overall though. They've pretty much declined steadily from the start sadly.
Daredevil Season 1 - Really solid throughout. A break-through for superhero television. Great villain, good story. Did end on a bit of a bum note though.
Jessica Jones - Messier than Daredevil, a bit padded and inconsistent. Strong core story with another fantastic villain, only this time it ended well.
Daredevil Season 2 - Excellent when Punisher is involved. Boring when Elektra is there instead. Like the first season it has a limp ending.
Luke Cage - A pretty much perfect early run, but as mentioned, the showrunners messed up badly killing Cottonmouth and then added insult to injury by replacing him with the campy, awful Diamondback. Never quite recovers from that, but I still enjoyed the other characters' stories.
Iron Fist - Garbage. Danny is badly written and performed, and the story crawls toward a boring conclusion. The Hand have always been a terribly underwhelming villain. I did enjoy Harold and Ward Meachum, for what it's worth.
Defenders - Only 2 episodes in so far, but somehow I'm liking this even less than Iron Fist. Danny is still awful, and I resent every time we cut away from a superior character.