Ambercup squash looks like a small, slightly-flattened pumpkin. Its orange, finely-textured flesh is sweet and dense, and not watery.
Buttercup squash have a thin but hard rind. Inside, they have finely-textured, orange flesh that is dense, not watery, with thick flesh walls, with a taste described by some as close to that of sweet potato.
Turban squash is perhaps better for use as an ornamental. It is edible, but the flesh doesn’t have much flavour at all. The closest most people seem to have come to suggesting it as a food item is as a soup tureen.