monohydrate is what all the big research is on. The other forms may have benefits if monohydrate doesn't agree with you, but they don't work any better.
Creapure is probably the most highly manufacturer of it. And I believe is the only form that isn't sourced primarily from China, so is having a price break due to the supply chain issues. (creatine got real expensive there for a bit, not sure if it came down)