In terms of mainstream presence it's pretty undeniable the answer is Drake. I swear you couldn't go anywhere without hearing God's Plan, Nice for What, In My Feelings, Nonstop, I'm Upset, and others as well as being featured on songs like Sicko Mode, Mia, Look Alive, Walk It Talk It, Yes Indeed, No Stylist.
However if it's a question of who I personally thought had the best year, I'd give it to either Denzel Curry (released Ta13oo which was my AOTY) or Kanye West (put out Ye and Kids See Ghosts as well as producing Daytona).