The 50 pound weight shuffle is a constant battle when flying to ports, which is why I really like the option I have to drive to Galveston with nobody ever weighing a bag. It is easier to bump over 50# if you have equipment like scuba gear to deal with. Its also harder on the return trip with added purchases (sometimes we pack a spare bag in our bag just to handle any overflow.
Another consideration is if it fits under the bed in the cabins. Most bags do, and duffle bags surely would, but I had a bigger hard-side I took on one trip that was too tall. I retired that one.