I like agger because he has the qualities I want in a defender. the reason I think agger is better is to me he seems the complete defender with ability on the deck and in the air. he also choses to position himself and snuff out danger rather than make well timed tackles which look great but have a greater margin for error. daniel seems naturally gifted to me whereas skrtel has had to work to improve, now skrtel has improved beyond all recognition and is clearly player of the season.
he (skrtel) is strong, quick and is now diving in less and less but I can't help but notice his form had dipped a little with the reintroduction of carra (maybe because he was/is being arsed to play on the left to accomadate the vice captain) so I think martin's imperious form has at least been 'helped' playing alongside agger. together I think they are the best centre back pair in the league, included the manu and city centre backs.
this is just an opinion though, and others may prefer skrtel because he has the qualities THEY want in a defender. skrtel is an ever present, he is very strong on the ball and he is not afraid to dive into a tackle and more importantly he is improving season on season. excellent qualities in a centre back. each to their own.