Epson Home Cinema 6100 Projector Screen Recommendations
If you want to lower black levels, then I'd recommend a high contrast light gray surface, but I'm figuring that many people buying the 6100 over the more expensive 6500UB, are the ones less concerned about black levels, including those who are more concerned about sports viewing.
Take all three into consideration. If your room has no ambient lighting issues, and you are strictly a movie watcher, then by all means a high contrast gray, or even a plain matte white should work best. If you have lighting under control, but want as bright as possible for sports, go with a screen with some gain.
Personally, I've been watching this projector primarily on my Firehawk G3, a high contrast gray (but expensive) screen. It's a very good fit for my room, and my mixed viewing. While in some ways the Firehawk is rather unique, consider screens like Elite's HC gray, and Da-lites HC Cinemavision, as similar type, but less expensive screens.