chemical
I just refinished a wood prop and used "Aircraft Stripper" by Kleen Strip purchased at an auto parts store. Paint strippers have been regulated to the point where they are pretty weak, but it did soften up the finish enough to remove it with a putty knife, and therefore avoid sanding and potentially altering the shape. Next time I refinish a prop I will do it the same way. I didn't strip the hub area because it was in very good condition from being covered by the spinner. If it has a urethane leading edge do not apply stripper to that area because it will soften. Carefully hand sand the urethane.
Tip - I wish that I had checked the static balance prior to doing anything because once down to bare wood it was way out of balance. If balance was checked at the outset I would have had a reference point.