I used 28mm (nikon 28ti, minolta tc-1), 35mm (nikon 35ti), 40mm (role 35 classic ti, plaubel makina 67 which is equivalent to 40mm), 50mm (summicron rigid DR) for the past 300 rolls and find the 28mm most useful for street photography.
28mm has the all rounder competence in street, the key is, get close to your subject and don't shoot from far away. It gives good wide view, powerful composition. When used at close distance, it's exaggeration will render the scene captive to the eye; when used from a distance, it's great for scenery shots.
40mm is a bit narrower, but role 35 has a great distortion that could give architecture shots an overwhelming power.
50mm for me is only good for urban still life shots. This is disappointing.
I just posted in another topic my experiences with several lenses, I'd like to cite it here:
In fact I forgot to mention that a good part of the My Angst serie is done by a role 35 classic titanium edition. It has the most competent lens I've used: fabulous contrast, very dark toned render of the scene, etc. I totally love it's 40mm lens, and I find it rendered the achetecture shots with mighty and powerful distortion. I know we usually don't use these terms when talking about distortion - we usually look for NO distortion. But this 40mm lens's distortion, when used properly, can give the architecture shots an overwhelming power.
I'm having a love hate relationship with summicron 50. The thing is, it's a bit narrow for me, and also this lens has its own character which is hard to control. I don't want people look at my photography and instead of praising the photography itself, keep on talking about how this summicron contributed to the aesthetics. So I find myself constantly, intentionally shooting things totally out of focus or with very slow speeds, because if in focus and tuned, the lens just come over me and render MY photography like other millions of summicron users. Also, I work a lot in post production: unconventional developing, usually very high push to gain grain and contrast to ensure people don't see that it's a summicron.
Also,I recently sold the mikon 28ti because I find it too big and clumsy. Now for wide angle I use a minolta tc-1. I did a search on this forum but didn't find any related topic on this machine. For the record: it's the camera of the greatest value I've seen (lens sold in leica m mount for over 1500 usd), and at the same time, a most fragile & expensive camera. It's lens totally surpassed anything in 28mm range, I abused mine with 100 rolls in the two month ownership. Now it's in japan waiting for repair (300 usd I presume including shipping fees). But I love it so much that I will totally pay this repair and (ab)use it again.