Both seem pretty relevant. I think a lot of vet schools have classes arranged so that histology comes first in the curriculum, but usually only by a semester or so. I would just pick whichever on honestly interests you the most!
You'll take both courses as a first year vet student. So I'd either go with the one you're most interested in, or maybe pick the one you think you'll have greatest difficulty in so it will be less difficult in vet school.