Obviously, if you don't/haven't run published modules in D&D, this is not the thread for you.
If you do, though, do you have favorites, and more specifically do you have one that you have run or played more than any others?
For the most part, I have only really recently started using modules as opposed to home brew adventures. That said, I have probably run The Sunless Citadel a dozen times in the 20 years (wow) since its release. It is my go-to introductory module, essentially my Keep on the Borderlands (despite the fact that I started playing D&D way back in 1985). It has all the things that make a great low level dungeon, including factions to deal with, horrible monsters, a potential TPK or two and fortune and glory to be won. Since it made it's official appearance for 5E in Tales of the Yawning Portal I have run it another half dozen times for folks trying to get into D&D. I much prefer it to Lost Mines as a singular adventure, though I think LMoP is a better introductory campaign.