It could come down to DC's chin. Since getting rocked by AJ in their first fight, he's had a grueling matching against Gustafsson, a rematch with AJ, and taken a knockout via head kick from Jon Jones. I don't know how much more damage he can take at his age.
With that said, my money would be on DC against Oezdemir. Not sure I'd say the same about a Gustafsson rematch. That was a very competitive fight and Gustafsson hasn't taken the same kind of damage since then, plus he's younger and still learning.