ZWK said:
In 0 PPR leagues I take Gronk over Graham, since he scores 1.5x as much as Graham in terms of VBD per game (historically). That is enough to make up for the injury risk. Graham will give you more games (in expectation) but probably not 1.5 as many.
In 1.5 PPR I prefer Graham, since Gronk is only worth about 1.25x as much as Graham in that format, in VBD per game.
Gronk's advantage is in touchdowns, so when you add more points for anything else that narrows the gap between them. Another way to look at it: in 0 PPR, 2 games of Gronk is worth 3 games of Graham. In 1.5 PPR, 4 games of Gronk is worth 5 games of Graham.
Exact numbers: In 0 PPR leagues, Gronk had 1.77x as much VBD per game as Graham last year and 1.44x in 2011. For 1.5 PPR, 1.28x and 1.21x. (Assuming 12 teams, no TE flex. Baseline ppg determined by sorting TEs by ppg, and going down the list until the total games played adds up to 204, which is 12 starting slots x 17 weeks.)
The relative VBD difference might change, but the absolute VBD difference remains huge. By my back-of-the-envelope calculations, In non-PPR leagues last year, Gronk scored about 2.9 points per game more than Graham (the number increases to 3.1 if you exclude week 17). In a yardage-heavy league I play (0.2 points for all yards), that jumps to 3.0 points (3.5 if you exclude week 17). In the crazy league I mentioned earlier (1.5 PPR + 0.15 points per yard for TEs only), the gap was 2.3 points (3.5 if you exclude week 17). I understand that the relative VBD difference tells us how many more games Graham has to play to even up their value (the smaller the relative difference, the fewer extra games Graham needs), but the absolute difference is what matters when they're both on the field (a 3 point VBD advantage is a 3 point VBD advantage whether you average 4 VBD a week or 40, and Gronk is averaging around a 3 point VBD advantage in all formats).
And like I said, Gronkowski is 2.5 years younger, which is a not-insignificant difference for dynasty, even if both are far from the downslope of their careers. I would say that I would expect Gronk to have more games remaining in his career than Graham, even with the front-loaded injury concerns.