Sanders.
Asik is a far better Center in terms of maturity, team help defense, being able to defend the perimeter, and overall great defensive anchor. And probably one of the best rebounding/defensive Centers not named Dwight Howard, Gasol, etc.
He also is less injured.
The problem is Sanders has infinite potential. I think CBS could tap into that, and really make him more excited. The Bucks are actually one of the worst franchises in my opinion... If you can get Sanders for the same price, you'd take it in a heart beat. Imagine a front court of Sully bullying power forwards, or stretching the defense by trying to shoot a 3, and then passes it to Rondo who immediately lobs it or throws the quick pass to Sanders who slams it down?
Bradley calling for a pick, taking a mid range shot he excels in, but somehow it rolls in and out only to see Sanders grabbing it and then put back dunking it?
Sanders in my opinion is actually a top 10 rebounder for PF/C. His long arms, and his great vertical along with his strengthened ability to tell where and when the ball will drop helps him in that category.
If anyone ever took Sanders over Asik, I would hope that GM would be fired.