If you are a non-knifemaker, then Micarta is a good choice. Reason being is, you don't have to flatten the material if you buy slabs. Micarta slabs I've used have all come flatter than the proverbial pancake.
On wood, I've found the slabs almost always have to be flattened on a belt sander or sanded down to get a true fit up to the full tang. Plus when you work the slabs to the desired shape, you can work Micarta with a regular dust mask. Not so depending on the wood as some woods are very toxic to work and can have serious sometimes life threatening side effects(Zebra wood and Cocobolo come to mind), use a respirator. Same with G-10. If you use wood, make sure you ask the seller if it is toxic. If you use G-10, use a respirator. Not using a respirator while working G-10 will land you a case of mesothilioma or lung cancer.
This really isn't intended to scare you. If you plan on doing some home handle replacement, I feel one should be informed as to what safety measures are warranted beforehand.
Good luck in this project!
All the best,
Mike U.