I guess I'm saying that I haven't seen enough of either to make a valid comparison.
It's my understanding (which is always imperfect) that Prima Agates in an original box are scarcer than even the Cerise Agates in an original box. For a while we didn't really know what the Primas looked like. Only figured it out recently (salute migbar!). And from some of the Pelt paperwork I've been lucky enough to see, we know that the Prima, along with the colored onyx (slag) and the Cerise, were the first three marbles that Pelt developed, And now that I have a Cerise box, I understand that I probably would need a Prima Agate box in my hands and a little time with the marbles to even begin looking for them elsewhere (free-range Prima Agates, I guess you could call them).
Going by photos only -- always risky -- they seem to have some similarities with the AAs, but they seem "cloudy-er," With some translucent white in some places. Maybe everyone should send me their Prima Agate boxes so I can know what the heck I'm talking about.