What makes a better hunting arrow for whittails
ash or douglas-fir???

both, any and all.. It really comes down to what You like..

River Cane.
When I could get a good batch of ash, I really like it.  TUFF!  Its a good heavy wood.  Takes alot of abuse.  Some folks, espically down here in the south east, have a hard time keep it straight.  I just checked my arrows, after they'd been sitting for awhile, and re-straightened 'em.
I've also used Doug. Fir, with execellent results.
It's just up to your peraonal preferance.

hey Brother i will second the Rivercane for hunting    its cheap its natures carbon if ya bust one no big deal.

Of those two choices and with your bows Ash will often go heavier than you want. Go with the fir. IMHO