I've played Rise of the Runelords, Curse of the Crimson Throne, Skull & Shackles, some of Council of Thieves, and single books of Kingmaker, Second Darkness and Shattered Star. I think the best one is Curse of the Crimson Throne. The best single part is the first book of Second Darkness. Rise of the Runelords has nice part, but the variety of horror genres didn't go down so well in my group. Skull & Shackles is very good, but has some awkward moments. Council of Thieves is great, but lacks a certain variety.
The overall best adventure path I have played is Savage Tide, tough that was for 3.5 and never published in books (it is from the pages of Dungeon Magazine). Overlong, maybe, but very, very good. If you end that adventure path once the players have safely defended Farshore or raided Scuttlecove, it might be even better.
So, in order, only the ones I played the majority of:
1 Curse of the Crimson Throne
2 Skull & Shackles
3 Council of Thieves
4 Rise of the Runelords