The Carada Criterion Brilliant White may be the best bang for the buck screen but the Stewart StudioTec 130 G3 is by most accounts the reference standard.
I have the StudioTec (1.3 gain) and a sample of the Carada BW material (1.4 gain) and the StudioTec is noticably brighter using my JVC HD100 (RS2) projector. So much for the gain game.