IMO, neither.

Try this- directly to your left direction (for RH shooter) hold up your hand in the flat palm "STOP indication" mannerism at full arm's length. Now slowly bring your hand towards your shoulder/face and notice which direction your elbow naturally wants to go. It's close to a 30* down and left for me- but everyone will be a little different. Try to bring your hand in and have your elbow bend only vertically (straight down), it is very unnatural and awkward. Same thing for having your elbow bend in the purely horizontal.

Your "natural" elbow bend direction is where you'll be the most comfortable (and repeatable). If you have to "force" into a form position, there's no way you'll be able to accurately do it time after time after time....