17mm. You'll not only get the street, but the alleys too

Seriously though ... wait that was serious.

No I mean ... I started doing street photos with a 50mm cause its all I had. Now I use my 28mm most days. But I also own a 35mm. When I can afford it, I'm going to get a 21mm.

From the OP about "having to get too close to the person" with a wider angle lens, well then you are just limiting your view of what street photography is. Its not always about a single person or a couple ... whatever. Oftentimes it encompasses the energy of "the street" as the subject, not people. Many of Friedlanders photos are nearly devoid of people, or they are small objects relative to the frame.

Now if you're interested in a kind of street portratiture, then sure a 50mm might be ideal .. but then I would argue engagement with the subject isn't always a bad thing.

Pre-focusing with a wider angle lens is easier too, and with the right camera you can stand right in front of someone and snap some shots and they'll never know, unless you are limiting yourself to looking through the viewfinder.

Have fun ... experiment!