Balsa is good for shallow running square bills that are lively and rise quickly to get over cover that you hit (which is what you want to do). Paulownia is similar to balsa in density but harder than balsa. It sometimes has crumbly grain that can be a problem. I use basswood for deeper diving baits, or sometimes white cedar. Basswood sands great to a smooth hard surface. Lots of woods can be used although some of the most dense/heavy hardwoods can be so dense that it is hard to build a bait that floats after the hardware is added. Generally speaking, lighter woods are more lively and that’s usually a good thing. IMO, it’s best to select just a few wood species and stick with them because it makes building easier when you know how a wood shapes, sands, is ballasted, and takes finish.