I like to use maple, poplar or any good hardwood that has a straight grain pattern. Thickness depends if you are adding bindings. Sometimes I will double up for the added strength, stiffness and depth. I takes more time to do this but for the way I build it is definitely worth it.
Thanks. When I worked for local luthier John McQuarrie of Northwood Guitars in 2002 he was very particular about getting the inside of the instrument as clean and nice looking as the outside. One of my jobs was the inside detail and cleanup and it rubbed off onto my instruments.