It all depends on what you want. I'd go with either Vault of Larin Karr or Grey Citadel.
VoLK: Small villages, wilderness adventures, Underdark/cave crawling, and dungeon crawl goodness. By the time my players got out, I was more than ready to have them travel. Some monster allocation that I found questionable (what was a Red Dragon doing underground, over 15 miles from the nearest Underdark entrance?) which resulted in a fairly major re-write of the module (also to bring it in line with my campaign's plot), but you could get by with less.
Grey Citadel: Well-designed city adventure, social/political intrigue, and dungeon crawling goodness. I almost wish I could have run my players through it, but they were too high a level after VoLK, and in the wrong part of the world.
But either would work very well.