The difference will be really minute to be observable.. But it will be good if u go for u2415 if u dont have problem with black bars... And also it has 5 usb (4 for u2414h) and little higher brightness but this really dont matter that much in real world scenario.. If you are doing color sensitive work then srgb and 1920*1200 will be good. The last good part is that it is cheaper.
Ultimately i think it comes down to what u want video vs productivity.. If u dont have problem with balck bars choice is clear go for little higher resolution.