Hi straightnlevel.
Jepps v DAP has been done to death a hundred times on Pprune. Try searching the posts (see search between FAQ and Forum Home above)
Cowhide v Duraflow? All i can say is that i bought a couple of 2" cowhide binders (with aus contents + 6 month amend) for $200 s/hand 5 years ago, and they have survived absolutely appalling humidity, sweat, beatings and other 'top end' thrashings and still look good and still are soundly holding all that knowledge together.
In fact they look even better than when i bought them!
Make friends with pilots who are about to p!ss off to Cathay or similar. Worth the extra bucks for leather.
ITCZ