Get the unrated version.
Antoine Fuqua (the director) originally envisioned this movie to be an R rated, gritty movie along the lines of Braveheart. He was 6 weeks into shooting the flick when Disney decided they wanted to use Arthur as their "Family Christmas movie", thus they told Fuqua to make the movie PG or PG-13. Fuqua was PISSED and almost walked off the set.
So they struck a deal, shoot a PG-13 movie for the theaters, but continue to shoot his "grittier" version for a special DVD. Fuqua put his heart and sole into the unrated version, not the theatrical release.
So get the unrated version.