Thomas over Horford would be a huge gamble. There's no doubt that in a perfect situation, Thomas would be better. He'll score, grab boards, steals and blocks, and offer decent-great %'s. But his situation is anywhere from perfect, and he's going to be battling for time, even if he plays well, because of Gooden and Noah.
Horford is the guy you've got to go with. We know where he'll play and he's going to get consistent minutes. His inconsistency can be frustrating and he won't provide scoring, but going with his boards, decent steals and blocks are probably a more sound decision for the last months of the year.
So how much do you like to gamble becomes the question