Having read through the above discussion, I personally agree with the posters saying that Kolo Toure should be starting.
For me, Toure is the first name on the teamsheet in defence. If we're playing 3 at the back, I'd go with Agger, Toure and Sakho.
Yes, Agger has made a couple of mistakes recently and has been quite poor in terms of marking players on set pieces, but Skrtel isn't some kind of unmoveable force just because he's had a couple of good games (it helps him hugely to have the likes of Sakho and Toure to back him up)
Let's not forget his performance against City last season where he gifted the ball to Tevez and his many other poor games.
Best back three, in my eyes, is Agger, Toure and Sakho.
If we're playing 2 at the back, I'd be playing Toure and Sakho.
However, that is unlikely, what with Agger being vice-captain and all.
We should all just be really grateful that from now on, when Agger gets his inevitable injuries, we're pretty much covered with equal quality and don't suddenly look really weak at the back.