-Favors has way fewer fouls, turnovers, and 4 minutes less than Cousins.
-Favors shoots 54% and Cousins shoots 46%.
-Favors is a far superior and versatile defender.
-Cousins shoots 5 shots a game more than Favors.
-Cousins is thought to be one of the worst teammates in the league.
-Cousins is a far superior rebounder, has better court vision, and is a better free throw shooter and gets to the line more.
-I'd be interested to see what Favors could do if he shot the ball 5 times more per game.
I would not touch Cousins with a 39 1/2 foot pole.
You also have to take into account potential improvement. Favors has steadily improved each season and I could see him averaging close to 17 points, 10 rebounds, and 2 blocks next season. That's not to say Cousins won't improve, too, but I think he's a bit closer to his ceiling than Favors is.
Some more damn good points made in this thread.