For my perspective, what ever you like to use is the best whether it be Poly-C or Resin. What ever works best for you is going to be the best product for your covering job.
Personally I have never covered a balsa plane with glass before so I don't speak from experiance.
I do speak from fiberglass experience in general though. I was in fiberglass fabrication for ten years.
I do have a project coming up, TF Giant Corsair, that will be glassed.
I will be covering it with epoxy and light cloth. Epoxy and glass will make the plane stronger, there is no two ways about it. It is physically impossible for the glass/balsa combination not to be stronger. When you apply the resin to the glass the resin soaks into the wood making the glass, resin and balsa a single composite. No wonder boat builders have used balsa as a core material for decades and still do. Epoxy itself is superior because it has physical strength properties that the others don't. Here again boat builders use epoxy to add strength in areas under decking and such.
I understand that the motive here is to cover the plane to get a good paintable surface but epoxy and glass do add some strength to the balsa.
Applying just enough resin to make the glass stick and conform so you don't have any air or resin bubbles. Second coat fills the weave, then you can use primer finish.