The best map I have built I feel is a two way tie, by popular or logical belief because everyone has seen it, my best is Brokenshadow http://totalminerforums.net/index.php?topic=6432.0
I built it a super long time ago, but rebuilt it much better around two years ago. I hit over 400 rates, and earned demigods for it the original way by Craig placing them. It's a RPG adventure map set in medieval time period. Definitely some amazing memories with it.
Why it's a tie, is because my other close favorite is my horror map. Into The Dark.http://totalminerforums.net/index.php?topic=11506.0
I've still yet to finish this because of needing more ideas and finishing the scripts to make everything flawless (created a year ago -__-) it's a very unique questing / adventure horror map, I loved building it and had a super fun time even playing it. Brings back nostalgia for whatever reason too.
Scripting and story wise, Into The Dark is my best.
Quality builds, exploration and amount of stuff wise, Brokenshadow is my best.