Both are likely to be undervalued in fantasy. It will be interesting to see with Rodgers, he's never really put a stellar TE year on the board, that I can recall, but he's also never played with Jimmy Graham. I'd certainly rather spend a mid or late round pick on either of these guys rather than a 1st or 2nd on Gronk or Ertz or whatever. It's even a more meaningful difference in an auction league. To be honest, when accounting for injuries and the cost to get either, I'd actually prefer to have Njoku on my team. Graham is getting older and has an injury history, Njoku wins on both fronts there. Based on name recognition and team situation, I'm sure Graham will also be drafted much earlier as well. Unless you're in a league with a bunch of Canes or Browns fans, not a lot of people will be fighting you for Njoku. Njoku is the better value. I know, fantasy nerd alert.
At the end of the day, both are going to be pro bowl TE's this year, you can quote me on that. Remember when Jordan Cameron broke out a few years ago? Who predicted that? I did and rode him to the moon.
When Olsen, Graham and Njoku are all in the pro bowl this year, good luck to anyone trying to recruit against El Sicario del 904 for that position.