Of these, my favorite is probably PoL. It's vague enough that I can toss things in all willy-nilly, but still packed with thematic conflict.
Next is Eberron. Eberron is good times, especially in 4e. 3.5 Eberron always felt like it was fighting against the rules, not working with them.
As for the Realms, I'm just really not a fan. I have some friends who love them and that's fine, but I prefer not to play there.
Then comes Dark Sun. I really wanna like Dark Sun, but I tend to be a bad match for it on some level. Every Dark Sun game I've ever joined has gone something like this.
Player 1 wants to make an Elven Rogue, a shifty, shady dealing pickpocket.
Player 2 wants to make an escaped Mul slave who was forced to fight in the pits for other's amusement.
Player 3 wants to make a Shaman, a guardian of the earth's natural ways who seeks to depose the Sorcerer-Kings.
I want to make a Shadow Bride of Nibenay, who actually enjoys her position and works in the best interest of the state.