I think Mourning would be the best bet. Up until his injury he was actually having a very good season. He isn't the same intimidating force that he was 5yrs ago, but he is still dominant in the paint. Mourning may be willing to play for the veterans minimum and more importantly on a yearly contract.
Ratliff WAS considered the best shot blocker in the league. His chronic knee ailments have seriously debilitated his abilities. He would still be better than Curry, Frye, James & Butler defensively...but if it were between Mourning & Ratliff, I would chose Mourning hands down.
Martin's HUGE contract, deteriorating athletic abilities and BAD attitude are a serious turn-off. Karl & Brown are Smith disciples and are from the same coaching mold. If Martin is having problems with Karl, you could only imagine how things would turn out with Brown who is older and alot less compromising.