Google it. In some cases the vert obscures the windage turret and in almost all cases the horizontal split obscures the elevation turrets if that is critical to you. Vertical seem to torque the scope less during the final tightening, but this could be my technique.

For some reason projection-less and then vertical split seem more aesthetically appealing to me, but that is a matter of taste and personal experience.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli