Best, as others have noted, varies with the user. A fast lens (large maximum aperture) will always be useful - but is not essential. A small lens can be useful - but is not essential. I usually use a less than tiny 17-250mm omn an APSC camera. It has seldom been of vast disadvantage. I also sometimes use a 50mm. f /1.8 prime - about as small a lens as there is - and I find it of no great benefit size wise. A prime lens may be "classic" - but reduces your options. If you want to be 'arty' or to pursue some subset of possible photos, then a prime may meet your needs. If you want flexibility to deal with anything you may wish to photo graph, then as wide a zoom range as possible is desirable. Street photography usually does not emphasise utter lens performance or adherence to rules - contents and inter-relationships usually predominate over absolute crispness of focus, spot on exposure of rule-matching framing. So while having the best that Carl-Zeiss can make would be very nice, a kit lens may not be too bad a start. Starting with your 17-55mm kit lens, equivalent to a full frame 26 - 83 mm will be a good start. I mostly use an 18-250mm f/3.5-6.3 on an APSC body = full frame 27mm- 375mm. The topn end gets used less often than the 18mm, and most photos would be in the 18-100 (27-150 equivalent) range. Very few people will recommend a 17 or 18mm lens and it is often cited for producing purposeful distortion, but I find it superb for super closeup 'fly on the wall' photos. With experience you can 'shoot from the hip' while walking through a crowd of people, or raise the camera slightly, and stand right in amongst a group of people - as invisible or visible as you wish to be. Sure - people see a tourist with a biggish camera, but you are not obviously an "in the face" photographer. Too too close and you get perspective distortion. Back off a small way and it becomes acceptable. The following examples will not all be at 18mm. but this is the sort of shot you could typically get with the 17-55 kit lens. Larger version - Windows: right click and select open in new tab. More anon maybe ... ![enter image description here][1] [1]: https://i.sstatic.net/wt2n3.jpg