Personally I think all the dogs that you mentioned are great, Jen. I have a GSD mix, but have had pure bred GSD in the past and they have all been wonderful. And I have not met a Dobie or Rott that I have not liked. And like others have suggested, gotta love the Mastiffs (although my 2 personal mastiff faves are the Alpine Mastiff (St. Bernard) and the Neapolitan Mastiff). The key with any dog is Training Training Training, and any dog can learn basic stuff right from the start.
So stick with training, giving your dog a "job" to do (based on the particulars of whatever breed you choose), and not letting it get away with stuff and you should have a totally wonderful obedient dog.