Miller can create offense, Hayes is a non-impact player.
Nonsense. Miller is the higher upside offensive player and is most effective in a vacuum (as in, with bad linemates Miller would produce more than Hayes with bad linemates), but Hayes is the better defensive player and is certainly an impact player. Ignoring contracts, it's a coin flip for me, but my team needs defensive prowess more so I lean toward Hayes. If I am looking for top 6 offensive more than top 6 defense, I choose Miller. With contracts I take Miller. Hayes was the one major change for the Flyers this offseason, and they went from being one of the worst teams in the league on the PK to one of the best - that's pretty substantial evidence of Hayes' impact.
I'm also not sold that this year's Miller is sustainable. Both are 45-60point two-way forwards for their careers, and I would expect the same kind of pace moving forward. Miller is given favorable zone starts this year at 52.3 ozs%, though he has also been given more favorable zone starts in the past with little boost to his scoring (16-17 he had 43.7 ozs% and 56 points, 17-18 he had 56 ozs% and 58 points). Hayes has had unfavorable zone starts of 44.4 ozs%, and has shown that ozs% doesn't affect his scoring much as well (44 point on 42.7 ozs% in 16/17). The mark of a good two-way forward is overcoming zone start percentage disadvantages, and that anyone can put up near zeroes for corsi, fenwick, and around 100 pdo with 42.7 ozs% is incredible. Also, I HIGHLY doubt that Miller will be even a 55 fo% going forward from here, since he is in no way elite at faceoffs. His current face off % is 61.4 (career ~50), and 60% is in the Claude Giroux, Ryan O'Reilly, Patrice Bergeron, Sean Couturier "Best in the game" territory. Losing even losing those faceoffs to go back down to norm will decrease possession for the Canucks and lead to a decrease in points moving forward. Hayes is approx. 48% at faceoffs for his last few years, and is pretty much exactly there now.
I like Miller a lot, but 60+ face off % (career ~50) and some outlier numbers would indicate him slowing down from this pace. His ATOI increasing should have a lot to do with total numbers increasing, but I would think a slight increase from his 17/18 year (58points) would be expected and the norm for him. But who knows? Let's see if he has this other level and keeps it up.