Definitely Horford, who can either hit jumper if he's left open, or easily find the open man as a result of the double team on Isaiah.
I knew Horford would be a good passer when we got him, but I didn't realize how good he'd be at finding the open man. I'm sure a team will try to hound Isaiah early on in a series, but if we're healthy, I expect they won't find it effective, and shortly give it up but for an occasional surprise possession or two.