Vellum.
There are a couple of recent threads here on the board (within the last week) about choosing what to use for paper piecing, but the requirements are basically the same - stable, viewable (transparent for placement), printable, and easily removable.
I don't think Golden Threads Paper comes in sheets or is printable, but if you were drawing your design, that would be an option, but pricey. Clear & Press is cheaper and more readily available.