The revised D&D 30 Day Challenge! - Day 7

My favorite edition is the Moldvay edition of basic.  Although I haven't read the expert rules, I am sure they are quite good as well.  The rules are simplistic and they allow a DM to modify things quite easily, add subtract etc.  There was no real campaign setting that is discussed within the book.  Basically there wasn't a lot of assumptions made, which was good.  

You can grab these rules at DNDclassics.com 

Runner Up

Although not technically an edition of D&D, but an amazing clone, Basic Fantasy is one of the best games I've played.  It has the same feel as the above B/X edition, with some nice extras like ascending AC.  There is a ton of modules, and extras at their site. 

Grab it here

www.basicfantasy.org