I tested a lot of them!
I recommend Deeper Shadows of Amn, but maybe not installing the full
package, I had troubles with the vampires AI.
Also there's a newer version for the improved dragons.
Fortunately, the readme details which files are involved in each
improvement, so just choose and copy in the override folder.
The Improved Kangaxx alone is really wonderful, and the added archlich
battle is maybe the hardest encounter you can face with a party
(not all the party members can resist or be shielded from 4 or 5
Abi Dahlzim!!!!

)