I have always voted for El Abd but the performances of Greer partnering Upson against Palace and Forest leads me to think that is the best central defensive pairing and there is no reason to change it..
GG for me, leadership and better distribution. AEA is capable of filling in almost anywhere along the back line (to varying degrees of competence) so is a more useful sub.
I asked the same question a few weeks ago when Greer was injured and most people voted for El Abd, which surprised me. I guess Upson has helped both centre backs look better when they play with him.