Dark blue vest can give people a sense of stability and maturity, especially in formal occasions. With white or beige clothes, you can make the dark blue vest more eye-catching; Pairing with clothes of the same color can make the overall collocation more harmonious.
Light gray vest can give people a low-key sense of elegance, and different colors can show different sense of fashion. For example, with black or white clothes, you can highlight the elegance of light gray; With light-colored clothes, the light-gray vest can be more conspicuous.
Generally speaking, the choice of which color vest looks better depends on personal preferences and specific matching needs.