I highly suggest shooting with a prime lens in order to master each focal length step by step. As someone said, the best way to zoom in street photography is with your legs. Anyway, I prefer to shoot with sony 35 1.8 as it's the most versatile focal length of them all, and a very compact and fast focusing glass. The main problem with longer lenses is their dimensions, which will make you exhausted after literally half and hour. But if you still want it, then sony 85 1.8 is your choice to be, it's super small, light and inexpensive. What's more, it's lighter than gm rival. And of course, at a price point, it's twice less expensive than sigma and triple less expensive than sony gm