In order from -A to -C, the amount of crosslinking decreases. That's why you can use expansion fittings with -A, it remembers its original shape or it wouldn't shrink onto the fittings and make the seal. It's the only one that can be recovered from a kink without having to cut the kink out and using a fitting. TO do that, you need a heat gun which allows the memory to help it return to original shape easier. Any of the pex tubing will be stiffer when it's colder and more flexible when it's warm. If you're looking for neat with pex, you may have chosen the wrong material. You do need some clamps to hold it, and it will droop a bit if it gets hot.