This was tough.
Josh has been in the league a few years and has developed pretty well, though he still has a few holes in his game. He is also a tweener that gives flexibility, but probably could not play full-time at either PF or SF. That withstanding he is a homer, has flash, is better marketing material and he can change a game on both ends of the court. If he had a reliable shot, this would be easy. I sometimes question his decision making.
Horford is a good, big man which is pretty hard to find at the NBA level. He has a high bb iq, is a true PF that can play pt at C. I believe that with the same years in the NBA as Josh, he will be one of "the" dominant PFs in the league. He has heart, skill and a winning attitude. He is also cheaper right now.
I went with Al, because I think he will eventually get us more wins with his inside game. Also, I believe a team should have a better shooter at the sf position than what Josh has shown thus far.