@jamigibbs For me it depends on the stresses I foresee the cabinet facing. Generally, for things that hang on walls, I put the pin boards horizontally, as pulling them through the tails would be difficult. Pulling the tail boards off the pins, would be comparatively easier (assuming a complete glue failure).
But I also cut my dovetails with chonky pins, which I think look better on the sides of things, rather than the thin pins which are the fashion.