Phil, on the technical side, PO will give greater printing speed. On the personal side, I developed both pt/pd and Kallitypes in both PO and ammonim citrate and found that the PO developed prints had better "depth" and a smoother tonality.
I then proceeded to try and mix PO and ammonium citrate in different ratios to see if I could gain the speed and depth of PO and the cooler tones of the citrate and found that there was no in between, the prints with one or the other developer were better than those with the mix.
IMO this is specially true with Cranes platinotype, the prints made with this paper and developed with citrate were rather weak and drab.....nothing like the prints I am getting with PO and socorro paper.
As I told you, alt printing is very "personal", Arentz gets glowing prints with platinotype, I just cant no matter what I do.....