Captain Obvious is wondering why no one has mentioned that these cards are variants on each other. Perhaps it was obvious enough that it didn't need mentioning? Besides, I'm sure many of us figured that's kinda your job at this point
Both score for prestige, and produce prestige for developments and consuming goods. PG Affluence is stronger on develop. FedCap is imho slightly stronger on consume.
Other stuff includes...
--PGAs extra bonus pts are definitely possible, but I've found myself scoring primarily from its PP bonus.
some notable differences to me include..
--if you want to double the pts that PP gives and you had a choice between the 2, Fed. Cap. is cheaper than PGA.
--For some cases, all the benefits of PGA are killed by the fact that it's so expensive. Building PGA will mean they'll never recover from it.
--pIII makes FC free while PGA still requires 3 cards with pII
--PGA comes with a PP. That can make or break certain games