>>9091045Vertical is better. It not only lets you get more expressive with pistols, but it improves shouldering poses with two-handed rifles as well. Notice that when properly holding most rifles, your wrist naturally cocks downwards a bit.
Vertical hinges also improve knife/sword poses, allowing you to point and stab like a rapier. There is little reason to wave a sword left and right like a fan, so horizontal hinges are nigh-useless there.