What Teneban was describing is called "windboxing" and yeah, it's pretty gross. Especially on Lucas and Ness because one look push can miscalibrate their entire recovery, making them go flying in the wrong direction. I really don't see any applications for Razor Leaf anymore other than poking.
B-air is substantially better than F-air if spaced correctly. You get the benefit of the range, better knockback, next to no punish if you space it correctly. F-air has good range and racks up damage pretty easily for comboes. One of the basest and my most favorite combos is just a F-air, double-jump, N-air.
I'd also like to bring up the D-tilt. This move is particularly good for setups and essentially tripping your opponent at low percentages and knocking them up at higher ones. It reaches further than her jab, just not as high. D-tilt to N-air/Up-tilt juggle is pretty good.