Yes, everything above. I think most people use acrylic because there are a couple of main brands with plain, very consistent worsted weight yarn in a BUNCH of colors, so it is super easy to find exactly what you want, plus, for the most part, the yarn is interchangeable between brands. It’s cheap, can be purchased almost anywhere, comes in a bazillion colors, 100% washable, and overall a good choice. But for me, I prefer a cotton, or even a wool. I have used Knitpick Pallettes for amigurumi and really liked the finished results. It is a finer yarn, so everything will be smaller, since a lot of amigurumi patterns are for worsted. But it comes in great colors, is affordable, especially on frequent sales, and it’s easy to get since it comes to you. But it isn’t as washable (it will felt) and working smaller may not be awesome if you are already getting hand cramps.
I find that a lot of yarn manufacturers list the same mm size of yarn hook and knitting needle as the recommended, but in my opinion, crochet should always be worked with a larger hook than it would as knitting due to the nature of the stitch. So, working on the recommended hook is, to me, already working on a hook too small for the yarn. I typically go down only one size for worsted weight, and not at all for finer yarns. This may help you with the hand cramping, as it sounds like you might be a tight crocheter already. The intention is to make smaller gaps between stitches, but you can overcome it in other ways, like lining the pieces in pieces of like-colored old sock, tights, nylons, etc. Work how it is best for your hands and wrists and don’t fret over it.