Between a 21 and a 28, probably the 28. I say that as a guy who has never really been very fond of the 28mm focal length.
Not really "street" but kinda/sorta streetish, in my previous incarnation as a news photographer, I used 180, 85, 35 and 24. I skipped the normal in those days. Later as a non-working photographer, my lenses have mostly hovered around the 50mm. While I have 20/21mm lenses and even a few 28mm lenses, I'm best served by a 50mm, a 35mm and a 24/25mm. It's a nice, tidy kit. Tossing in something between 60mm and 85mm gives a little more breathing room. I just ramble around taking pictures of general subjects wherever I happen to be.
Two final points--These days, I mostly use APS-C Fuji X-Pro cameras with Zeiss and Voigtlander lenses. You gotta work with close equivalents there. And I really, really love the look of the 20/21mm lens.
But, given the circumstances, I'd still pick the 28mm here.
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