For now I'm going to say Toronto, and I'll be watching our games against them closely.
They used to be a really bad matchup for us, but I think our new personnel addresses our old vulnerabilities - we should be able to keep them from killing us on the boards late in the game, and I think Jaylen is going to give DeRozan all he can handle. Demarre is good enough he can't be totally stopped, but Jaylen is a tough, tough matchup for him.
I wouldn't sleep on the Wizards either. They are such a strange team - capable of coughing up games against pretty mediocre teams, and then playing very very tough against the best.