You also inquired about what material would be durable. For years, most decent backpacks have been made with synthetic cloth, most typically nylon, which is virtually immortal in anything like normal usage. The weak spot in any pack available today is the sewing and the seams. This is not evident on casual inspection and one reason for checking the warranty/return policy.

Durability will be significantly influenced by the type of trips you contemplate. Will you be bush whacking through rugged terrain or strolling along the Appalachian Trail? Carrying climbing/caving/hunting gear?

For really heavy loads and longer trips, consider an exterior frame pack, like the classic Kelty packs. For heavy or bulky loads in moderate country, they are unsurpassed, but modern internal frame packs are more versatile and just about as comfortable.

Whatever you buy, it will not be cheap. Shop carefully and rent or borrow first, if at all possible.