Well, you saw the difference in the offense without him being 100%, and I posted earlier this year that Gronkowski's presence is as important, if not more, as '07 Moss in terms of opening up the game for other players. Jimmy Graham was not too far removed from Gronk statistically, but that offense ran through Darren Sproles and Graham isn't half the blocker that Gronk is. Calvin Johnson is obviously a complete beast who is virtually impossible to stop. Although he doesn't bring to the line of scrimmage the same types of problems as Gronk, it's hard to argue against Megatron. There are also a few running backs with great versatility like Foster, McCoy, and Rice. Mike Wallace gets an honorable mention for becoming a more complete receiver, but he's not as valuable as these others. But in the end, I think it has to be between Gronk and Calvin Johnson. Who would you take if you could have either one of them?