ORIGINAL: Rodney
I have found that, for prepainted or colored material, Solartex (or any of the fabrics ending in tex such as Worldtex, colortex, etc.) is the easiest to work with. For unpainted, Ceconite (the lightest grade) from Aircraft Spruce and Specialities, is the easiest to work with but you have to provide the adhesive for the Ceconite.
Poly-Span (similar to medium silkspan) and Poly-Span Lite (tissue like) take my vote. They need a balsa prep step with something like Balsarite (org solvent)or Balsalock (water based). They are then ironed on.
Take 3 coats nitrate or butyrate to fill and are ready for primer. I supposed the water based polyU could also be used to fill, but can't vouch for that method
Some free-flighters will cover with PolySpan tissue and come back witha layer of Esaki Tissue (rice husk paper) for a pretty tuff super light covering. Great thing about Esaki is the full assortment of dyed colors available. Great for open bay wings, stabs or stringered fuselages.....