when i choose to use paper i like velum, or paper piecing paper- but wash away foundation paper is WONDERFUL! it is easy to see through- tears away well- and what is left washes away easily-
i don't like printer paper because it is stiff- and more difficult to tear away- also stiffer to fold and sew on-
most of the time i use a lightweight stablizer or muslin- and leave it in- but if i decide i want to remove- i really prefer the wash away.