Generally in this hobby/business, we call these mallets rather than hammers. Hammer "implies" a steel head which should not be used on leather stamps.
Poly mallets are fairly light weight, rawhide may be heavier depending on which size you buy. They have quite a different feel to them. When I started tooling in 1961, I used a wooden mallet that my grandfather had made. As you beat it, little wood fibers start to flake off the face and get trapped in your tooling if not careful. But that is what I could afford, and used for many years. I kept one face clean for other work and just beatup the other face. Had to shave a bit off now and then to reduce the hollow in the centre of the face.
I prefer the rawhide mallet. Still have the wood mallet.
Tom