All of them!!!! Being a little biased, with family who flew in Lancs, I would say that. For me, the operations against the Dams are the most daring raids in aircraft of the entire WWII campaign. The raid against the Tirpitz was also astonishing.
worthy of mention, no single raid in particular, the day and night raids over Germany superb and the bravery staggers belief. Lets hope everyone ignores the lively discussion topic mentioned sadly about dresden and others.
Finally, but, not least, the fairy swordfish guys who took on the Bismarck and disabled her so the RN could dispatch her to the bottom of the sea
Mitch