Fitz and Wallace are must starts, and Britt has shown me nothing to make be believe otherwise at this point either. All 4 are honestly must-starts in 3WR formats, but since you have to choose I'll bench Smith as a gut call
Fitz. Reason being that Wallace has been over 100 yards in each game, same for Smith and Britt will feast against the Broncos just like AJ Green and Jerome Simpson did (over 120 a peice). I think Fitz and co. could get up early and they start running more. That is quite the foursome of WR's you have though.
You definitely start Fitzy and Wallace, as for the other 2.... man, tough one. I guess it comes to passing volume and I think Tennessee is going to try and run more, especially against Denver's soft D-line, and to get CJ2K more work. Panthers and Jags could actually be a closer game IMO, therefore more passing.... So I'd bench Britt.