Don't buy a USED bow..... you don't need someone elses problems, especially if this is a bow that you plan on shooting for awhile.
Of the brands you mentioned, one of THE most popular and affordable bows in 2011 is the BowTech Assassian. Smooth, fast, quiet and an awesome rock steady back wall. I would be certain to shoot one of these against any other bow you may be interested in ?!?
Obviously the best advice would be to NEVER buy ANY bow sight un-seen. Head to a Pro Shop and shoot as many bows as you're interested in and I promise you, one bow will stand out as just right for ya.
Good luck and good shootin'