sniki
Well-known
Only one filter: yellow-green
...if I had just one B&W filter, it is one that I don't think is manufactured. I would like a vignette filter.

Listen to the brother. Yes, there are situations where this filter isn't appropriate, and the biggest drawback of any filter is filter factor, but for b&w this is the most useful filter 90%+ of the time.
Exactly the only two B&W filters I have. Both B+W MRC, of course. They have "enough" of an effect--not so light as to be hardly noticeable (such as light yellow, etc.) and not too strong either (like the reds).Listen to the Brothers!
B+W Yellow-Green.
Next choice: B+W Yellow-Orange.
If you could choose one black and white filter for street photography, what would it be? I am thinking Orange.
Yellow-Orange or Yellow-Green. From B+W. Fortunately, I am not limited and own both. And several step-up rings. I can use the filters on several lenses from 34mm to 46mm.
I do have K2 (medium yellow), orange & red in other sizes. The Yellow-Green & Yellow-Orange see the most use.