I want a bottle that fits in my hand easily, so I don't struggle to hold it when I'm using it, my hand doesn't cramp up because it's having to stretch so wide, and it doesn't slip from my hand when it and I are all soapy and my eyes are closed so I can't see what I am doing.
I want at least one flat surface so it will stand on the side of the bath without wobbling or tipping over. I am less bothered by something to hang it with, but if it has that (and many people will use that, ) it must be fit for purpose, so won't break easily, can cope with the weight of the full bottle hanging from it and so on.
I want the lid to fit so that I don't get soapy, slippery drips round the bath/shower and don't waste lots getting a useable blob on my hand or washing implement (sponge, flannel, loofah, whatever.) I would like it to be openable with one hand, but not to the point that the top breaks off really easily. I want to be able to get pretty much every last drop of the stuff out of the bottle before I throw it in the recycling, so I don't want a shape which encourages pockets of soapy stuff which won't come out easily.
None of this is relevant to whether I am short or tall, fat or thin, totally average or anything else. I want good functionality, not a reminder of body shapes, particularly if this is at the expense of everything mentioned above.
(And yes, scent, quality and affordability are also important factors - which again, are not at all relevant to my size and shape.)