Do we actually know who wrote Letho, Jacque and O'Dimm? To me, those three are the best.
I have no information on that, but it seems the majority of the larger quests in TW3 were written by these three people:
Arkadiusz Borowik (also a TW2 writer): Pyres of Novigrad, Get Junior, Carnal Sins, Forefathers' Eve, The King is Dead - Long Live the King, The Battle of Kaer Morhen
Jakub Szamalek: Count Reuven's Treasure, Missing Persons/Nameless, For the Advancement of Learning, King's Gambit
Karolina Stachyra: Bloody Baron, Family Matters, Possession, Broken Flowers, Coronation