"Which one is more correct?"
FWIW, and this is not the acid test, but a Life-Like HO MP BL-2 appears to match or approximate the darker of the 2 blues, above. Of course, some simple Internet research on MP diesels/BL-2's should yield the answer.
Paint fades, and if the lighter blue Wms is incorrect, some basic and enjoyable weathering with Bragdon's dry pigments could yield a nice "dirty, faded, in service" look to it.