I'm enormously privileged to have visited Schott NYC's New Jersey factory to get the ULTIMATE GUIDE to picking a leather for your jacket.
Should you go with heavyweight, midweight, or lightweight? Cow or horse? Lamb or sheep? We break it all down here. Basically, horse is the densest, sheepskin with the wool is warmest, calfskin and lambskin are soft and easier to break in and more consistent looking, goat is as strong as cow but less consistent in appearance, suede and nubuck are less tough and need something applied for water resistance, and cowhide reigns supreme: heavyweight is tougher, lightweight is more comfortable from the get go, but remember you're probably not wearing them on motorbikes so the 'durability' aspect of thickness probably doesn't have much practical significance for most guys.
Lastly, the way leather is processed can be just as important for comfort/durability/appearance as what animal it comes from, so talk to your leather jacket manufacturer for tips.