I'd say Greg Monroe. Al-Farouq probably won't live up to the expectations his draft number imposes on him, but I think he can become a fine role player.
I think Gordon Hayward is fine--his jumper's solid enough, and he's a better athlete than given credit for. The fact that he plays a mutual exclusion offensive game will only help him as well. He's a good team player, and I think he can even be solid defensively in this league.
Orton might bust out due to conditioning/foul proneness/attitude? problems, but it won't be because of his game. While he's not quick or vertically athletic, he's very long, can play center effectively in this league and has great instincts in disrupting with his steal/block combination, and his defensive impact is decent. Rebounds the ball well too. Offensively he fits the part with his ability to dunk and tip in at a good rate for a center, and has a budding jumper which he also takes quite a lot of (can go either way though). But still, enough tools on both ends of the court to be a good player in this league.