The best cameras for street photography are those that are reasonably small and unobtrusive. If people notice you with something big and professional looking with a large telephoto or zoom lens stuck on the front they could become wary of you and as soon as you raise the beast to your eye they will already be avoiding you.
Smaller format cameras such as APS-C are popular as they can be more discrete.
Medium focal length prime lenses are the most popular for this type of photography for several reasons; they are smaller and so can keep the size of the camera down; they are easier to use; they can improve your photography.
Keeping the size of the camera down means that it is easier to keep one in your handbag or manbag or even in your pocket, ready for use at any time.
Not being a zoom lens means that you won't find yourself wasting time by zooming in and out to find the best framing before you take the shot - and possibly missing the moment.
Using a fixed focal length lens means that you need to think more about the composition and about being in the right place. It makes you see more and think more.
The most popular medium focal length lenses used for street photography are 35mm to 50mm prime lenses or their equivalent, such as 23mm to 35mm in APS-C format.
The 35mm focal length gives a slightly distorted slightly wide-angle field of view but gets a little more into the shot than the 50mm which has a slightly narrower field of view but without any distortion and is similar to what the eye normally sees.
With a Single Lens Reflex camera system or a Mirrorless Interchangeable Lens camera system, a choice of
lenses can be carried for different situations. Or you can be really brave and take a camera and one lens. Or just take a fixed lens camera.
My favourite street camera is one of the newer Fujifilm X100 series cameras. They are slim, high-spec, all-metal, APS-C cameras with a fixed 23mm f2 lens. Mine lives in my bag or my jacket pocket and goes everywhere with me.
I also like them because they have an optical viewfinder and an electronic viewfinder as well as a rear viewing screen and because of their retro styling they have the look of an old rangefinder film camera. Nobody is going to take much notice of you with a camera like that.