From a street photography perspective, if I'm in a crowd, a party, a festival, or indoors the 23mm is better as it's easier to fill the frame in those situations. If you're just walking on an uncrowded street it becomes more awkward to shove a camera into someone's face, and you may be shooting from across the street, so I find a 50mm better. Of course this is just in general. There are cases where you'd do the exact opposite of what I mention, but I've found those situations to be the exception.