Whomever stays the healthiest over the 82 game schedule will lead the team.
Hall will probably have the highest ppg... but there's a higher than average chance he misses some games... especially now when he'll probably play even more balls out to keep up with McDavid.
Eberle plugs along and puts up pts consistently and I think he's a safe bet if he can avoid injury. He's also guaranteed big juicy minutes on the RW and on the PP as I think both Purcell/Yak are a clear cut below on the right side.
RNH will likely have a strong season as McDavid becomes the defacto #1C which should give RNH a little more breathing space as opponents will likely focus their best defense on the Hall/McDavid line (if that combo stays together). Assuming RNH essentially becomes the #2C though... he'll have slightly less juicy minutes and I don't think he'll lead the team in pts.
My pick (by elimination) is Eberle.