I like National Balsa. I use their standard wood. Im not competing so it works fine for me. If you pay the extra for their Aero Light you will get what they claim. Its going to run from super light to 7lbs. I watched Sparky's review on National Balsa and he complained a lot about his purchase as he weighed each sheet but in the end, they promised under 7lb wood and that's what he got from what I recall. I get his point that he was hoping for 4lb wood but that's not what they advertised.
I am amazed we can get balsa wood at all for environmental and social reasons. There are some great videos on YouTube that show the harvesting and production of balsa in New Guinea. I appreciate every piece I have in hand.