Yew tends to be lighter weight than Osage.
yew is very good in a D style bow, but i've seen many flat bows. Also made a few Osage bows, both D shaped longbows and flat bows.
all preformed very well.
yew was easier to get in WA when i lived there. Osage is easier to get where i'm at now...
both are great bow woods.
from my experience, Osage is easy to work with dry heat, yew is easier to steam.
either way, i think it boils down to what is easier to get a hold of...