Hope I'm not too late to contribute my experience. Just came back from Thailand, where I had a short try at street photography at their night markets. As they say always pick the right lens for the job. I carry the 450D (i.e. APS-C) with a 50 1.8, 18-55, and 10-22.
For the night market, which is what I take to mean street photography, I mostly stuck to my 50, or switched to the 10-22 for an "overview" shot. The prime is fast for this kind of low light, and with F1.8 it really isolates the subjects from the background which is very much required since the entire scene is very crowded with things and people that will distract viewers from your intended subject. That's the advantage of a good prime (although my prime isn't exactly a good one)
As for 50 or 35 or whatnot, it depends again on what type of shots you do. I find the 50 very useful on my APS-C because, it's less intrusive. You can snap pictures of people without them noticing. But I do mostly half body shots at max, and never do full body, so 50 is rather essential. If I were to use a shorter lens, I would have to get closer, and that would mean I would be noticed.
But, at AFA, where I was shooting cosplayers, they were posing for others to get shots. In that kind of situation, a load of photographers are crowding around a subject, and it's difficult to control framing because if you move forward, it's not good etiquette to block others, and if you move back, you would be blocked by others. 35 would suit the typical distance that most photographers stand from their subject for that situation, and get a full body shot, or a zoom for even easier framing.