On the long run, yes, resting is better than holding tight. Cause holding tires very easily whereas with resting, you kinda rest it on the bones instead of using muscle. Muscle=movement!
Its very important to relax yr left, resting, arm and hand as much as possible. Less tremors=easier aiming and less fatique.
Hów you rest it on yr hand/fist, is very personal, and depends on the gun (balance) and personal build.
Also, do you use the hunting stance?(=with elbow loose from body) or target?(elbow rested on hip/rib cage?). Target one is MUCH more stable and less fatique.
Also, have you ever tested it for ammo?