Replace the plastic safety button on the Mossberg with a steel one and it will outlast anyone using it for defensive purposes (based on the inclusion of the 590A1 in the OP).
I much prefer the 870 but that is due to long familiarity with them. I've owned and used both models and really don't see much difference for general use. Now, if this is to be a dedicated trap or other clay gun, then it's the Remington for longevity but more importantly, various easy to find and relatively inexpensive accessories to better fit the gun to a specific purpose.
