Maple action wood. Ive done some heavy duty testing in some of the harshest conditions Alaska dishes out. Have never hand any delamination or other problems that using softer woods and mixing dissimilar woods can bring.
Built a bow in 1992 without tip overlays using action wood core and under glass and put a twelve strand fast flight string on it. Purposely dry fired it over ten times. Leaned it against a tree on Kodiak Island for a full ten day hunt. It poured down rain for nine of those days. Hunted moose with it the next season and used it to whack the brush while calling (do that with My favorite as well). Anyway... you get the picture. It took the abuse and is still a shooter.
There are purdier woods to put under glass, but for strength, uniformity, and durability, you cant beat action wood. Im with Ian... bamboo's my second choice as well.