Are hard or soft luggage more durable as check-in luggage?

It varies between manufacturers and brands.

From my experience, both are just as durable. It’s just a matter of finding a the right brands.

A well made soft case suitcase is less likely to tear over time. Airlines often refuse to check in luggage with noticeable tears for obvious reasons.

A soft case should also have a sturdy frame which is key to it’s longevity.

A well made hard case is less likely to crack. It should also have wheels that run smoothly. 4, 360° swivel wheels are standard.

From personal experience a soft case is going to be just as durable as a hard case of the same quality. What a hard case does better than a soft case is that it will protect fragile items and distribute weight better because of the two main separated compartments.

Some might argue that a soft case is lighter than a hard case but from my experience they can way the same if they are made well.

People often underestimate how much a good suitcase should cost. I can vouch for my Nood (NZ brand) soft case suitcase which is still tear-free after 10 years. Not once have I ever used a suitcase cover on it. My hard case Samsonite suitcases have also withstood a few years of air travel and have yet to show any signs of structural damage. I do use suitcase covers on my hard cases to protect them from scuff marks