With the cloudy, milky look of water based, you might not be able to tell if it yellowed or not. With heart pine floors, or with most stain colors for that matter, you will never notice any yellowing.
I posted to the board of one of the major manufacturers of both water and oil based poly about adding a hardener to their water based. They told me that I was a lot better off to use oil based as it was a lot harder and more abrasion resistant. That was enough for me. I vote oil based.