First Romana. She could hold her own against the Doctor. I always preferred the stronger companions, instead of the ones that follow him like a puppy dog.
Actually she got pregnant and left the show because she wanted to have more time with the baby. Plus I heard she felt that the producers were turning a once strong companion into another classic "lady in distress".Same here. I take it she (Mary Tamm) was not so popular with the producers. Pity as I enjoyed the good-natured sparring - the Doctor certainly had a match. For the same reason, I think Jenny would be great to return as a companion (a bit reminiscent of the first Doctor traveling with his granddaughter I guess). While not quite the "looker" as Romana, she certainly could make a great match with the Doctor IMO.