Do you really need GWF? That's like a 1/2 point extra in damage right at the cost of 2 or 3 in AC?
You don't need GWF, sword+board is interesting as well, but GWF is definitely the highest DPR option. The big difference is the polearm mastery feat giving the bonus attack, so you can apply hex damage again.
There is the question of if GWF applies to the hex damage die. We are playing it does, since other similar rules like critical hits double hex damage. I don't think there has been an official ruling whether it does or not. If you play with it applying to hex, it ends up being approximately the same damage increase as the Duelist option, so it seems balanced to allow it.
At level 6 (with extra attack):
Long sword with duelist, +2 str taken at level 4:
With hex up:
(d8 + 4 + d6) x 2 = 24 DPR
Polearm with GWF, Polearm mastery feat taken:
First round (putting up hex, so no bonus attack):
(d10 + 3 + d6) x 2 = 26.92 DPR
Once hex is up:
(d10 + 3 + d6) x 2 + d4 + 3 + d6 = 37.08 DPR
Without hex at all:
(d10 + 3) x 2 + d4 + 3 = 24.6 DPR
Also comparing to EB:
With hex: (d10 + 4 + d6) x 2 = 26 DPR
Without hex: (d10 + 4) x 2 = 19 DPR