I have used both epoxy and Poly-c.
Epoxy is normally a two coat process
Poly is, for me at least 4 or more coats to fill the weave.
Both have garnered very good results.
but remember! poly-c is water based, and what happens when balsa is wet? It becomes soft and absorbs the water. This is why you have to seal the wood with some sort of sanding sealer. It will seal the grain of the balsa and the poly with not be absorbed. Use at least two coats of sealer and sand with 400 after its dry.
And best of all......you can finish the entire airframe in a day.
Good Luck