Not caring for the on-line Diablo game play Hellfire was my favorite single player version. We did play Diablo vanilla mulitiplayer on LAN often having several servers going at one time.
Bringing a new class, two new characters and other enhancements made [url=http://en.wikipedia.org/wiki/Diablo:_Hellfire]Hellfire[/url] the preferred off-line version for Diablo . . . at least with everyone I knew. . . =)
Edit: For those who want to enable the extra quests and multiplayer in Hellfire I believe
this link will give instructions for doing so.
I also have two more commands in my command.txt file that are not in the download file.
nestart;cryptart;
-Added at the end of the string. I have forgotten what they do but the Hellfire wiki says the following about nestart
"nestart -- Enables a different palette for the Hive. Try the game with and without this option to see the fairly slight difference." I assume it would do something similar for the crypt palette.