As far as the best, for me it's a toss up between Bushwick Bill's "Everclear" and The Geto Boys "Geto Boys & Girls". The main reason I love these tracks is because they're both true stories. In "Everclear" Bushwick talks about how his eye got shot out, how they took a picture of him on the way into the e.r. for the G.B.'s - We Can't Be Stopped album, etc., and all that shit really happenned. It also contains what I think is the best line in the history of rap music, "It's fucked up I had to lose an eye, to see shit clearly". And in "Geto Boys & Girls", Scarface and Willie D talk about how they basically started a war in Houston when Willie D left the group. The story goes that a mutual friend of their's mother begged them to squash it after the friend was killed behind the beef. Eventually they "sat down and settled our differences like men".
But here's a few honorable mentions:
Biggie - Niggas Bleed
Outkast - Art of Storytellin'
Eminem - Stan (I know it got played out, but still a great story track)
Tech N9ne - Trapped in a Psycho's Body
Scarface - Never Seen a Man Cry
Jay-Z - Moment of Clarity
Devin the Dude - I Can't Quit
UGK - Feds In Town
Pimp C - I'm Free
Too $hort - Survivin' the Game
Yukmouth - City of Dope