I'd rank them as follows for the ROS:
Thomas - normally I don't like having a pair of WRs from the same team, but Peyton's play makes them fantasy-relevant a la Nicks and Cruz for the Giants. Speaking of which...
Cruz - as you said, when Eli is right then Cruz gets his #s. I think the dealbreaker here is the QB -- Peyton > Eli
Cobb - no doubt has been awesome. The risk is when the receiving group is at full strength come fantasy playoff time. IMO, this is still a spread-the-wealth passing game for Rodgers a la the Saints passing game. As far as Cobb's return game goes, opposing teams can choose to kick/punt the ball away from him to limit his impact in that respect.
Hope this helps. Regardless you have a good problem and any of them would be a great option.
Please help me out with mine? viewtopic.php?f=18&t=530117