I have owned working line rotties. Im on my 4th.
I have handled Dobes, and knew a breeder.
IMO:
I like the solidness of the rottie.
Walk the 2 dogs, and one feels like gliding silk (dobe) and the other a well oiled combine harvester.
The rottie is naturally a velcro dog, and herder. So they dont run off.
The dobe behaves like a sight hound, and takes off. Ive met a LOT of dobes with poor recalls for owners, you dont see that in rotties generally.
The dobe is more independant and lays on a bed.
The rottie will forgo comforable bed,to have its head resting on your foot.
Rotties body slam as a form of play, and can send a dobe rolling 4-5 times over and over like a cartwheel lol
Rotties are leaners. And have a full body lean that will knock over something that is say under 5 ft.
Both are great deterants