I find that a narrow crotch nappy fits better under pants, but they are not always as good for containing newborn poo. Having said that, AIOs are not generally brilliant for containing newborn poo, because you don't have the extra added layer of defence - ie: nappy and cover. But I used BumGs and Berry Plushes from birth, and never had a blowout. I've had one blowout from a d'lish, but it was an extremely scary poo.

Wide or narrow crotch nappies suit different bubs differently too, I know some people have said that a narrow crotch fits their wide hipped/bummed baby like a g-string.

Generally speaking, the trimmer the nappy, the less absorbent. Ittis seem to be the exception to the rule, as they use bamboo as the absorbent layers, and they are well designed for maximum trimness.

HTH!!