Wish I could tell you, but I have no experience with either, I think the Radway Green that Aim Surplus has is berdan primed (non reloadable) and is from the mid 90's. The Port I think is from the mid 80's and I think it's boxer primed. I ordered from AIM because of positive past experience, but I may try to scrounge a bit more money for some of that Port too.
As for the NATO stamp, Australian ammo didn't have the NATO stamp, but from my experience and what others say it was pretty good stuff. IMO the NATO stamp guarantees its will be at least of a certain quality, but the lack thereof doesn't guarantee inferior quality necessarily.