You only mentioned 12 or 25, so I presume u have a budget.
I would say go for 25, because your 12mm is well covered by the 12-50. Generally speaking, you do not need that 1 and 2/3 stop for wide angle unless you really need to freeze motion.
The 25/1.4 will be more useful as the 25mm on the 12-50 is having an aperture of F3.x.or F4.0+/- and you will gain like 3 stops for street shots. It is also cheaper at $800 new compared to $1000++ for the 12/2.0. Resale value holds as it is more in demand and out of stock recently.