Horford is an elite PF/C.
Crowder at PF gives us a huge offensive advantage while not really limiting our defense (he actually he helps it with his ability to switch anywhere).
Kelly is an average starter, and one of the better bigs in the league off the bench.
Amir is a serviceable starter and above average big off the bench.
Zeller is an okay big off the bench who can start if needed, but he's one of the best 3rd stringer/injury replacement in league.
Mickey is developing, and though he hasn't shown much on the court, he has shown potential, and not only as an able defender, but also as a serviceable player on the other side of the court.
Jerebko is debatable....and arguably inconsistent in terms of being a major part of our rotation....but when he's playing well, he's a huge asset in our offense, defense, and versatility. I think with some more aggression he could probably be a strong player for us, and with some luck/confidence he could be a championship-caliber piece of the puzzle.