If you use a chainsaw you get the best amount of gatherable resources... (ie: Prime Hide, Prime Pelt, Prime Blood) it just will depend on what you kill, to get the larger amounts. Lower tier alpha's will not drop as much as the higher tier ones. (Alpha Rhino's, Mammoths, Spino's, etc) drop the most that I have seen. Megapiths' are hard to harvest due to their spawns eating their bodies after they die. But in general, you'll want to harvest with a chainsaw. (Scion's drop a decent amount as well.... but if it's pelt/hide you're after... Rhino's and Spino's are your safest bet).