I think this depends on where you're drafting, and who the best available RB/WRs are going to be with your first couple of picks. I agree Hopkins and Gordon are the first two. If you're picking near the end of the first round (technically 4th round, after keepers are kept), then you'll be one of the first people to draft two players and should (in theory) be able to round out your RB/WR groups with those picks, so I'd keep Hill as third.
If your 2nd (5th after keepers) round pick is projected to be weak (due to late pick, so many players kept/drafted by then, etc) that your RB2 or WR2 is going to be weak, then I'd keep Ertz just to solidify having a top 3 player at the TE position.
Sounds a bit backwards this way, but I usually approach TE in a draft like this: as long as I feel like I'm finding values at RB/WR in each round, I'll happily keep drafting them and wait for TE. As soon as I find a round where I feel like taking a RB/WR would be reaching at all, that's when I go TE. By projecting out who is kept and who will be available, you'll be able to sort of map out your first two or three picks, get a sense of what type of players you'll be looking at drafting. If you find yourself hating your options or feeling like you'll be forcing yourself to take a RB/WR before you should, then I'd keep Ertz. On the other hand, if you like what's available at RB/WR there, keep building up those positions by keeping Hill, and you'll still be able to draft a TE (maybe even Ertz) somewhere else.
