It's a matter of preference, really. Noah is longer and taller than Horford, but Horford is just as good as Noah at putting the ball on the floor, he's a better athlete, stronger, and, unlike Noah, shows signs of a promising post game and mid range jumper. He already has a lethal spin move that he uses to get by his defender at will, and his jump shot, while inconsistent, has very good form and is much improved over last season. He even drew Karl Malone comparisons from some scouts in the offseason. That doesn't mean he'll be a Karl Malone, but he has the same type of game as the Mailman.
Horford's rebounding, defense, and ability to run the floor, on top of his promising, yet developing post game, should firmly entrench him into a top 7 pick, and he could go top 5 depending on how workouts go. I can tell you that his game against Oden while playing on a hobbled foot really helped his stock, though. I was at that game and sitting next to some of the scouts... they were thoroughly impressed.
Again, it's a matter of preference. Noah's probably a slightly better player for the Suns' system, and will be a good pro himself. I think Horford, though, could eventually develop into an NBA All-Star, I really do. He's got all the tools, and is a very smart player.
