lyrically Em wins hands down. on every collab that has Em, it's him that rips the song apart. On SROM There they go, it's Eminem that kills the track, Jay-z's rengade, Em is better, IMO, ( and Nas' ) and so on. Em just shines out brighter. But telling a story, it's probably equal.
Obie tells about his hood and growing up, him being shot and the violence in Detroit
Em tells about his childhood, his wife and daughter
Both tell great story's and have a definitive feel to them but overall I think Eminem is better than Obie