I always refer to Vehicle body ratings for size.
A Doberman drone has a body of 3.
A Dodge Scoot (think a Vespa Scooter) has a body of 4.
If you want to ride a drone, having the equivalenet size/body of a Scooter sounds pretty reasonable, so IMHO a Doberman is just too small.
Upsize to any of the Body 4 drones, and I think you're all good.
Note: The smallest vehicle that can carry a humanoid is the Ares-Segway Terrier (Body of 2, and is indeed a Segway 2-wheeler). This would lend weight to the argument of having as smaller drone do the work, buts seeing as the Segway looks like it will break apart from a strong sneeze, I don't recommend it for shadowrunning...)