My current bokken is Maple. I made it so the maple was a very nice piece. I like the comprimise of weicht to strength, and the feel of it is just right.
My current Jo is Ipe. Very heavy and quite strong, but I made it with about 7/8" Diameter. It is finished a deep burnished brown and has a wonderful feel.
I have made some bokken from this also Nice and strong, but you feel the weight after a short time.