Petal (and short) wide-angle, round (and longer) for normal to telephoto. It's about the angle that the lens can "see", you don't want it to include the lens shade in the image. For short lenses or wide zooms the exact length and degree of cut-away at the corners is very important to avoid vignetting. With lenses of 100mm or more the design doesn't matter much.
BTW, there is nothing more infuriating than using your widest lens to compose a shot and then finding that the corners are dark and you have to crop 10%+ off each edge, turning the field of view of a 35mm lens into what you would get with a 50mm one.