Well, I'll break with the pack. Background: I am playing Shackled City right now, I collected Age of Worms with the idea of running it, and am doing the same with Savage Tides.
I am enjoying SCAP, albeit we are playing the book not the Dungeon modules. I like the fact that you get to see disparate threads drawn slowly together to reveal the scale of the threat. Lots of different foes, acting for different reasons.
AoW started interestingly, but then appears to get stuck in a rut. By having a definite foe involved from pretty early on it seem to repeat itself interminably. I know some can't help getting off on having ancient Greyhawk references resurrected, but they hold zip interest to me. So all told - to me - AoW is the weakest Adventure Path.
STAP is interesting in so far as it involves so far a very natural progression of action, and uses the environment well. My only 2 concerns are that
(i) it might feel a bit too much of a rail road to the players; after the early stages if the players want to act outside the framework of the adventures it might be tricky to fold them back into the adventures;
(ii) from a personal perspective I don't like adventures that cut PCs off from civilization for so long; it deprives them of options.
All this said: I am very glad for the APs; they've raised the bar of standards required for a decent campaign.