I honestly hate running modules because as others have stated the prep time is far above and beyond what I have to do to make my own stuff. Still, in my own sandbox world I’ve used for years B1 and B2 exist and serve as “fuck I totally have no idea what is going on this session” ass-saver locations, albeit cut down a bit.
If I have to actually pick one, again it’s going to be a toss-up between B1 and B2 simply because the first one showed me how to key a dungeon properly (along with help from the Mentzer red box DMs Guide dungeon) and B2 which laid the groundwork for a small sandbox campaign. A lot of the other TSR modules are easy to use for one-shots because most of them are from actual tournament games and have a definitive start->end. Many, many more modern adventures seem to gloss over this to some degree and expect you to either include the module as part of some overarching metaplot or as a cog in the “adventure path” you’re running. Makes it Not Easy to run without shoehorning a lot of crap in, and at that point why not make up your own shit?