pressing A is better because its an attack and it also cancels out the lag. neutral B leave you vulnerable for a few moments
Not necessarily. While you do have a valid point, pressing B instead of A when you're gliding near the edge can sometimes mean the difference between SD'ing and not SD'ing. Also, like I said, if you don't want the momentum that you have in your glide atm (for spacing purposes, SD-avoidage purposes, etc), then B is a better option. While, usually, it is safer to go for the glide attack, you shouldn't just automatically press A every time; B has its uses, too.
By the way, Veng, if you don't want to attack, but you still want to keep your momentum (for whatever reason), you can press A, like, 1 frame (or as close as you can get to 1 frame) before you hit the ground. This will make you hit the ground before the glide attack comes out, thereby making it so you don't actually glide attack, and it will still cancel the lag because you are, technically, in some part in the glide attack animation. This isn't as easy to do as it sounds, though, since MK's glide attack comes out fast...not that I'm saying that it's, necessarily, a hard thing to do, but it is a tad frame specific. Just wanted to throw that out there