Spruce is a better choice than basswood, but it's gotten very expensive. If you build a wing properly and fly it as intended, you won't break wings, so you don't have to change the design by using different woods.

There's no easy way to explain when and why you would use basswood or spruce instead of balsa and what size to use, etc. There are just too many variables involved. Most of us figure out what works by building a variety of kits. That gives us enough experience to know what to use in what situation.

If you have a specific application we can give you specific answers.