I like smaller natural ones and if they're fake c or d is fine. Big natural ones = saggy. Small ones can help a woman shave a few years off if they're perky. Once they start to sag from age she can spruce them up a bit!
LOVE big tits, big is D's and higher... C's are cool too, but not quite as much to wrap around for tit jobs sometimes. Little tities have sensitive nips, so they all have plusses, but for overall pleasure, big ol' titties are hard to beat...