Having the two side by side full size is really the only way to do it. While you can compare samples and point out differences, it doesn't give you any idea of how they will look full size. Also of importance is projector placement. If you are comparing screen materials with the projector on a table but your final goal is to ceiling mount or otherwise, it will look different - especially when comparing viewing angles - than the final install. Point is, when you are testing try to get everything positioned the way they will be installed. Not feasible or desirable for a lot of people but its the best way to get a true representation of how the materials will perform in your room.