^^^^^^
What he said. About the only difference between the Maverick 88 and the Mossberg 500 series is the location of the safety, and although I prefer the 500, it's not a deal breaker. I prefer simple shotguns for defensive work, not a lot of bling. For instance, I don't like ghost ring sights. If you need those you should have grabbed your carbine or rifle. But I do like a BIG front dot. I think the Magpul rear stock is wonderful, except you do have to dremel it to be able to remove the trigger group (easy to do). I kinda like the old-school corncob forend on the Mav 88, actually.
The 590 and A1 were built to US Army spec, and yes, they are beefier guns. However, is that necessary for civilian use? Probably not. An Army armory gun would be shot a lot by many people over many years. I've never heard of anyone wearning out a Mossberg 500, which the Mav 88 basically is. I'd save the money. Because you mentioned the 590 I think it's safe to assume you are looking for an HD shotty, not a clay breaker.
Instead of the ammo, I'd get the Mav 88 (either barrel, I like the shorter, but some like the 20", personal preference), and ...
- Magpul Mossberg SGA 500 stock
- XS Big Dot front sight (or TruGlo lightpipe style if you like those)
- Magpul forward sling mount
- Magpul MS1 Two-Point Quick-Adjust Sling
- Magpul Industries Paraclip
- Velcro 5 or 6 round shot card for the receiver
I'm going to guess that complete setup will be about the price of the 590, but it will be an awesome HD shotgun setup.
This photo has a little different selection of parts, but is close to what you'd end up with.