Don't know. Depends which body and friends we're talking about.

My only personal experience with three or more long term companions is Thirteen's initial crew, which compels me to say; no more than two please.

A group (this includes the Doctor) of two, three or four is ideal IMO. Four and you sometimes have the issue of finding something for them all to do. Two and you sometimes have the issue of turning them into a double-act. I know Moffat said he always preferred the dynamic of a trio, but I couldn't find much evidence of that in his writing. Three would probably be my vote too though.

I'm not sure the wording of your options is very clear. "A duo" suggests the Doctor is one of them, which would be the same as your first option.

My favorite eras happen to include 2-3 companions. It allows for more varied personal interactions, instead of just Doctor+companion.

I’d say 2-3 companions is my preference, but the writing has to be up to it. Chibnall would’ve benefited more from having just Yaz, I reckon.

This feels more memorable...

Good luck keeping up the quality while trying to keep a good dynamic between 9+ people.

I think 1-2 is probably best, depending on what sort of stories are being told.