Brightness is affected by many things not just the screen. Room size, room ambient lighting, distance of projector, type of projector, just to name a few. Also, keep in mind most screens with a higher gain have problems with contrast and color. But my suggestion are for you to get samples of these four:
Screen Innovations Black Diamond
DaLite High Power
My preference, and yes I've seen all four, is the Black Diamond. I like the way it handles ambient lighting, contrast, color and overall brightness. Plus, the aesthetics of it are a nice touch. But again, these are my opinion which is why I suggest getting samples and testing them in your environment.