For low 3D where you are trying new maneuvers down low, foam gets my vote. Built properly it has the same strength-weight ratio of a balsa plane, but is much easier to fix when you dork your plane. I have a 3DFoamy.com SuperCap, which is made of foam, and it is awesome. Plenty of carbon to keep it stiff, it has nearly the same wing area of a .40 size profile glow plane, but only weighs a pound. I have crashed it a couple times due to an elevator servo failing, and also a midair or two, and each time it just took a little CA to glue the pieces back together. The G-force wing gives the same forward flight characteristics as an airfoiled plane, while retaining the amazing 3D performance of a flat-winged airplane. It's the best of both worlds.