As it seems the choice is restricted to BPF and GMF I tried t compare those watches between themselves and with the Gen. Since unfrotunately I don't have any of those watches (only a Noob a version) I tried to find the best pictures I could find. The Day-Date model compared is a 40mm, white gold (steel) with silver dial.
In the following picture you see from left: GMF, BPF, Noob.
I would love somebody with experience to see if there is any visible difference between the GMF and BPF versions. I can't see any. The Noob seems to have the date more recessed than the others.
Ihe next picture you see from left: GMF, Gen, BPF.
Again I cannot see any significant difference, but as said I am not expert.
If anybody has been through this GMF vs BPF process, it would be really nice to hear the conclusions.