OK, here's the thing in NE. Hernandez is the pass-catching TE. Alge Crumpler is the blocking TE. Gronkwoski is the "in-between" guy. Against a team like Pitt, it's no surprise the two best blockers were in the game; Crumpler was doing a ton of pass-protecting, Gronkowski got most of his work in on play-action.
Basically, you have to think about the team NE is playing before deciding which guy to play. Against a team like Pitt, NE went with mass-protect or play-action to keep people off Brady. Against a team likely to sit back and play cover 2, you want Hernandez. Next week, I'm not sure who you want. Cover 2 favors Hernandez; the fact that I think the Pats will want to run the ball favors gronkowski. I'd probably go with Hernandez this week, since he's more likely to get "consistent" yards/catches.