Epoxy is stronger and I would use it in most cases for joining wings, putting on tail surfaces and firewalls and gear blocks, wing blocks for the wing screws to go into, stuff like that. You can get by with CA on some of those applications, but I would be a lot more comfortable with epoxy in those. The rest pretty much use CA. I have built entire planes with CA, but on power birds, I just like the strenth of epoxy in places like I explained.