Tough one. Chris Johnson seems due for a bounce-back season, and who could forget the potential the guy has to dominate fantasy scoring. But the titans have a very tough schedule against run defenses.
Jimmy Graham is arguably the no. 1 TE in fantasy, though. He gets a ton of targets, is a favorite red-zone target for a team that passes in the red zone at a high percentage, and he's so new to football that it's hard to imagine he won't have a growth curve that would lead to more production. LBs are not fast enough to cover him, and safeties are not big enough to guard him. Graham is a matchup nightmare, and one of the more unique ones in the NFL.
IMO, there's more upside potential with Johnson, because he could possibly rise up past the 1500-total yard mark, and he gets all the goal line work as well. But Graham is still very likely to be productive with less bust potential. He probably won't exceed las season's production by too much in a best case scenario, but it doesn't seem likely he'll fall too far short of it either, unless he's injured.