I see that most of you guys are using a water based poly.  What is the reasoning for this?

No chemical smell and a lot less volatile.

better finish no yellowing, easier clean up, and seems to dry quicker

agreed.....

No odor, easy cleanup.

For me it's mainly that the water based doesn't yellow over time and turn my white cap into a cream cap.  The yellowing is kind of nice over any wood stain though so if you don't use white it probably doesn't matter.

The no-smell trait is nice too.  I'm not sure if the oil offers better protection, but the water base seems to hold up well.

The only problem i've found with water based is on very dark wood it has a slight milky look.Thats furniture not bows though.

I find the water based poly holds up against wear much better than wipe on Min Wax poly, plus the other benefits already stated.I use Zinsser ultimate poly.

I like the water based poly-no stink and plenty tough.

Mushin, it looks milky on dark stained arrows too, the MW polycrylic does any way.

Eric