I would have to go with Sarah Jane and K-9. Probably equal. It almost seemed as if she didn't need the Doctor, except for his gadgets, and K-9 seemed to have a human-like wit.
Spoilers, if you haven't watched the second season of the new series!!!
It was great to see them return for the new series. Seeing the after-effects of a trip with the Doctor...well, I'll rethink if I see a blue box!!!
Anyone listen to the Big Finish audios? Some of the companions there are good. And it's great to hear some of the original actors again.
There is also a Romana spin-off, the Gallifrey Chronicles.....with Leela and a K-9 no less11