I can give you my argument for the Mossberg 500 so you can not talk to me any more either if you would like.
yes the M12 Winchester is amazing , and rather heavy , but I take it out of the running because it is no longer made and hasn't been for a long time.
The Ithaca M37 is also very nice but not really a player in the work horse pump gun any more either.
so 870 and 500
the down fall to the all steel receiver on the 870 is the ejector , it is rivetted in before the receiver is finished and it is the most major wear item on the gun and also holds the barrel index so the barrel wobbles and isn't safe to shoot with a broken ejector.
so this was a sort of problem but one that could be repaired with time and parts but it got very close to the value of the gun so then it made it for many a throw away gun and I hate throw away guns that when a part that should be able to be easily fixed causes the end of service for something that could keep going for a much longer time with how everything else is made
then , Remington went bankrupt and the part wasn't available
some years go by and there is apparently a aftermarket part that you drill out the rivets and the new ejector has threads and little screws so you don't have to scrap your gun for the wear part but it is more expensive than it should be and it is more work than it should be
the aftermarket part is 89 dollars and shipping
https://www.weaponsarmorer.com/product-p/sully870ejectorsystem.htmthe ejector on a 500 takes one screw , 5 minutes at home and you are back in business for 8.54 and shipping of a small padded envelope.
also a standard 500 holds 5 in the tube one in the chamber
the standard 870 was 4 and 1
I own both , I shoot both , I like both
but when functionality of working well for a right or left handed shooter (I have a couple in 20ga I used for teaching kids)
parts compatibility and availability.
a larger trigger guard for cold weather gloves
and a lighter gun to carry in the field
a Larger safety to get off easily (I use an oversized aftermarket safety) , the 500 is what I am carrying.
I shoot the same score with the 500 or the 870 in a round of trap. so these are the reasons I carry the 500 in the field.