1st: The Enemy Within Campaign - released by Cubicle 7. Without a doubt the best campaign I’ve ever played and DM’d. (I’m on the third run through!) Brilliant characters, setting and investigation. Locations are evocative. You could easily run it for 5e using the rules for gunpowder in DMG. The perfect mix of plot and sandbox. It also does a very good job of bridging the gap between local heroes and kingdom heroes. All you would need to do is convert treasure and NPC stats. You’d lose a bit of the old world flavor but the adventure is still at core amazing. Highlights include secret societies, carnivals, corrupt nobles, deadly meteors, mutants, lurking ratmen, imperial politics and small but vicious dogs. Run it, you won’t regret it. There is a reason this is on every top ten list of adventures of all time… the re-release is much better.
2nd: Age of Worms. The best of the 3e adventure paths. A really solid campaign of growing evil. Strong individual chapters and a nice overarching theme. Part One the Gathering of Winds has probably the best dungeon I’ve seen in a game for tier 1 characters.
3rd: Odyssey of the Dragonlords. Epic, campaign with a capital E. Heroes at the heart of everything in a great setting. Very thematic. Beautiful to read and to DM. Best Greek campaign I’ve seen.
4th: Way of the Wicked. Written for Pathfinder but easily convertible. It has may favorite hook for adventuring and has one of the best story arcs I’ve seen in a campaign. A pleasure to DM. Of course it is for an Evil Party, and the methods the writer uses to keep things coherent is very clever. One of the chapters the party get to build their own dungeon and protect it against adventurers!
5th: Curse of Strahd. The best of the 5e WotC hardbacks. A great tight story which links everything back to the BBEG. Very atmospheric and fun to DM. The only reason it hasn’t placed higher is that I think after the awesome 80% of the book, the castle is a bit of an anticlimax.
Honourable mention: Tales of the Old Margrave. By Kobald Press. Designed for 5e. Again very thematic and atmospheric. A series of beautifully written adventures that capture a Hansel and Grettel theme.
Honourable mention: Kingmaker. It was amazing for pathfinder 1e but had its flaws. A new release should be out soon which improves these and also offers a 5e monster and NPC conversion. Worth waiting for that.