What you want is a kinetic strap that stretches when a load is applied to it, which reduces the stresses and strains on both vehicles. You may also want to research the topic of vehicle recovery, and learn how to calculate the actual weight of a stuck vehicle, which varies depending how the vehicle is stuck.
To be safe though, get a kinetic strap that is rated for at least 15 tons- this will get you out of almost all sticky situations safely, and without damage to either vehicle.