RISE OF THE RUNELORDS: the strong adventures, for me, were the middle ones. In particular HOOK MOUNTAIN MASSACRE for the Kreegs, the NPCs and the lake monster scene. And the siege in the first part of Fortress of the Stone Giants.
CURSE OF THE CRIMSON THRONE. Edge of Anarchy is very very good, but SEVEN DAYS TO THE GRAVE is the "must play" adventure, with a unique context, strong roleplay with NPCs, and intriguing story.
KINGMAKER. A very strong beginning: both Stolen Land and RIVERS RUN RED are excellent. I chose the second as the best because you start the build your own kingdom minigame. The last two deserve to be played, too. Especially the sixth, Sound of a Thousand Screams, departs from the sandboxy feel of the other installments and is more a Lewis-Carrol inspired fairy-tale. A "must play", but even than, the two starting adventures are better.
CARRION CROWN. The first adventure, HAUNTING OF HARROWSTONE, has an intriguing plot, a mystery story, roleplay, and strong NPCs. A must play. So for the first half of the second adventure, Trial of the Beast.
JADE REGENT. I really appreciated the unique "Marco Polo's expedition" caravan experience in the third adventure, THE HUNGRY STORM.
SKULLS AND SHACKLES. All adventures are consistently good, and the first three are excellent. Perhaps RAIDERS OF THE FEVER SEA grants the most satisfying "pirate experience".
SHATTERED STAR. The second adventure, Curse of the Lady's Light, offers some unique opportunities. Anyway, in my opinion the true gem is BEYOND THE DOOMSDAY DOOR, a grand high-level megadungeon with interesting NPCs.
REIGN OF WINTER. This is my favourite AP and, in my opinion, each adventure is a must-play experience. The story and NPCs, the locations and even the enemies and objects remain consistently unique and memorable. At the beginning, with The Snows of Summer you got that feeling of immersion in a fairy-tale. That feeling intensifies and takes a distinct Russian flavour with the second adventure, The Shackled Hut. Maiden, Mother and Crone you descent in an incredible dungeon but also enter the esoteric world of the witches, and you meet the feminine archetypes. For me it was a deep, psychological experience. The Frozen Stars has a really unique setting. If the DM wants, he can work on this one; for example, I played that in the Star Wars universe. Now that Starfinder is out, it could be possible to reskin and play this adventure in Starfinder, and it would play great.
RASPUTIN MUST DIE, the fifth adventure, has the incredible merit to show that Pathfinder can be played on Earth, in an historical setting -in a modern setting with gunpowder! -, meeting and fighting against historical characters. I even reflected on the possibility of my PCs meeting with Lenin or Trotsky. The sixth installment, The Witch Queen's Revenge, goes deep in the world of mythoes, is rich with interesting set pieces and encounters, and concludes this incredible campaign in a very good way, but remains the weakest of these adventures.
Anyway, I'm really really happy to have played through all of it, this Adventure Path was one of my best roleplaying experiences.