I prefer a standing shot. I stand up roughly 30% of the time anyway, just don't get comfortable in most stands sitting although I have started replacing some old hand on's with stands that have the chair and man those are nice. Makes hunting long days so much more comfortable. My 3 best stands are those types now. I stand up as soon as I see a deer so I am ready when and if the time comes. Only time I would take a sitting shot is if I have no chance to stand up.
As far as height, I prefer 15-18 foot range. Much over that makes me nervous and I don't like the angle on close shots, so I keep it under 18'. I just make up for the lower height with picking stands that have some cover or I put some branches around to help hide me. Works for me.