All preference. I think jumping straight leg is pretty lame. Looks lame and the nose of the ski goes twice as high as you THINK you did. You also cant see your landing, just a nose and pole. I jump flat. We ride river, and I dont want the rear of my ski potentially smacking the bottom of the riverbed. Same I imagine should go for surf, though Ive never ridden.
When you land ass first, you have about a full second of the ski sinking before the pump grabs and you can actually throttle out. This is not the case landing flat. As was said before if you time it right, and gas it right, as soon as you touch the water with your ski it will hook up and take off. You can land sideways flat, you just have to know how to handle a ski.
Again its all preference, but damn, all those straight leggers, they SWEAR they get huge air everytime. Muahahahahah