What fabric is the toughest depends on what the fabric needs to be "tough" against. If it needs to be a garment that needs to be tough against wear, then yes, heavy weight demin would be the answer. If it needs to be tough against stretching, then a vinyl coated nylon would be best. If it needs to be tough against being cut, then Kevlar is the toughest.
While many people believe denim is very tough, the toughest fabric you can buy is canvas.
No not really.
Gingham
Tweed seems to be one of the most durable.
Leather sofas are the most comfortable and durable.
Most baby bedding is made of cloth fabric.
Poly Cotton is the best durable mix, 65% Polyester 35% Cotton, (Polycotton) standard everyday fabric
Cotton tee's clean the easiest, and jeans are most durable.
denim
A durable synthetic fabric.
Leather is more durable as long as it is quality leather.
Leather is usually the most durable, but if you get cheap leather and/or don't care for it properly, it won't last. High-quality fabric cared for properly would last better than poorly maintained, cheap leather.
Renu leather fabric is a composite of polyurethane, leather, and polyester. It is a breathable and durable fabric that is comfortable to sit on.
The best backpack fabric is the 500 denier Cordura. It is durable and very reliable in terms of waterproofing.
Most people prefer a cotton and polyester blend for durability as well as breathability.