I stopped posting in here because ths decision tied my head in a knot. I think I have ruled out the mossberg. But in its place is the Mav 88. The only thing I dont like is the lack of sighs. I intent to use it for mostly slugs. so sights are manditory. I would like to put a black hawk recoil reduction stock on it. I heard the Mav is Mossberg compatable. So hopfully it would fit, now all I need is to solve the sighting problem. do they come with sights. if not then I guess its leaves the Remington. which seems to have all I need. and more. Which makes me think I should just get it anyway and enjoy the flexability of options.
I wouldn't do that.
The 590 is a much better gun out of the box, about the only positive things I can say about the Mav 88 is that it functions reliably and isn't dangerous to use. But lets take a critical look at both guns.
The 20" version of the 590 is IMHO too heavy to use with optimal speed, but when equipped with a Side Saddle and Speed Feed stock it carries 19 rounds of 23/4" ammo, so you don't need to load up your pockets with ammo prior to leaving camp. On the other hand, if you haven't solved the problem with the first 3 shots your probably won't. If I was purchasing a 590 today, it would be one of the shorter versions, and I would carry additional ammo in a belt carried speed loader.
One problem I have with both the 500 and the 88 is the magazine tube does not allow access for cleaning behind the follower. Because a defensive gun must be 100% reliable, this is a non-starter for me.
The 590 and the 88 essentially use the same action although the 88 uses a cross bolt safety. IMHO, a cross bolt safety is less convenient than a tang safety, but you can get used to either. The Maverick 88 has the stiffest action of any out of the box pump action shotgun I've encountered. I had expected this to clean up with cleaning, but it did not. The action requires much polishing before it is anything like my 590 was after it's initial cleaning. With the action cocked and the barrel held vertically, pressing the slide release will cause the 590's fore-end to drop half way, and a slight bump on the butt will bring it to the end of it's stroke.
One element that led me to choose the 590 over the 870 was that the Mossberg's ejector is held in place with a screw and the Remington is riveted in place. In the unlikely event of a failure, I can replace the ejector on my 590 with no more than a screw driver, and there being no gunsmith close by this was an important consideration to me. Other than that, parts can be easily swapped out to keep either gun functioning. Both the 590 and the 870 will provide thousands of rounds of trouble free cycling, if they work properly out of the box. There have been functioning issues with individual guns from both manufacturers, but given the shear number of guns both companies produce, this is hardly a surprise. These issues are evident right out of the box, and although inconvenient, are normally easily fixed by the respective warranty depots. Having said that, a fellow at work had an 870 that came with ejection issues he was unable to resolve. Tod Bartell had a thread a while back about issues he experienced with a Mossberg gun, but I don't recall the specifics or the outcome.
The plastic stocks furnished by Mossberg are all too long, and that should be addressed before using the gun for serious work. I haven't followed my own advice here, in fact I put a stainless steel spacer behind the recoil pad of my 590 to protect the rubber from the Speed Feed springs, and the 88's stock still feels longer. Its been a long time since I've held a Marine Magnum but I don't remember it feeling unmanageable. An after market stock can provide a solution, but is an additional expense as well. IMHO a pistol grip stock does not provide a natural feel, a good cheek weld, nor encourage quick use. Of course I haven't had much to do with them since I packed around an FAL, so you might feel otherwise if you have more recent and extensive experience with military style stocks.
The 590 comes with an excellent ghost ring sight which is fully adjustable and protected by wings. The front sight is a rectangular post with a red face, but Mossberg didn't go to the trouble of protecting this front sight, and in my experience it is the front sight that is more prone to damage than the rear. The 88 comes with a bead front sight that is mounted directly on the barrel that will cause you to shoot high. If you were to keep the bead it would have to be mounted on a pedestal so that the height of the bead and the height of the receiver were matched. It is possible to do decent close range slug shooting with a bead front sight, but not if the bead is mounted too low on the barrel. In this respect, Remington has it all over Mossberg.
The 590 can be had with a parkerized finish, and I like this feature very much over blueing, chrome or stainless. It is resistant to rusting, and scratches can mostly be wiped away with an oily rag. The blued 88 will not stand up to long term hard use under difficult conditions. The condition of the gun will suffer quickly once the finish fails unless it gets better than average care.
Finally the 88 is designed to be a no frills security gun. That it is. The bead front sight is unacceptable, the action is difficult, there are no provisions for a sling and swivels, and the chances are that the LOP is in need of being shortened. An 88 could be made into a good back country defense gun, but this requires time and money that you might be unwilling to spend, and that should be spent on a better gun. The 88's size makes it handier and quicker to use than the 20" 590, but the 88's magazine arrangement remains a problem. The economy version of the 870 is a much better gun than the 88. Rifle sights and sling swivels can be mounted on the 870 resulting in a better gun for less money than you get by tricking out the 88.
A worthwhile consideration to the defense shotgun is the addition of screw in chokes. This increases the barrel thickness at the muzzle and makes the delicate thin wall muzzle more resilient to bumps and scuffs against rocks, not to mention that you can experiment to see which choke produces the best accuracy with your chosen ammo. The addition of a hand guard/heat shield will also provide some impact protection to the barrel, should the gun be dropped, or the individual who is carrying it takes a fall.
. I've carried them both for animal protection when walking the fields doing crop damage claim adjustments.
. This season I'm going to alternate with carrying an M1 Garand using 165gr Sierra HPBT handloads and will see how that works out on a comparative basis. 
