Each of the named brands have advantages disadvantages. Mossberg uses double extractors and an easily removed/replaced ejector whereas Remington's ejector is welded in....
Ithaca was once a "police standard" because of it's bottom ejection, very simple and "slick" operating mechanism, as well as lack of a disconnector that allows a trained operator to "slam fire" by holding back the trigger while pumping the action....very fast way to put serious lead downrange!
The Ithaca is also very compact.
Remington has the best mag tube/barrel idea which means one can add a tube extension without buying a new barrel or removing the OEM tube from the receiver.
But let me introduce another shotgun every bit as good and in many ways better...the Winchester 1897 or a modern production variant! Why? Because it's LIGHT...slender, compact, and even with an 18" barrel noticeably shorter than any "modern" design because the bolt retracts out the back of the receiver. It has an external hammer...EASY to note condition and no need for a safety. EASY to load due to the loading port being complete CLEAR, and just as easy to unload by releasing shells via external buttons. The gun is reliable, and certainly "proven" in combat.
But MY question is...if you're buying your own, why would you CHOOSE a pump action over an autoloader? I mean, this question, across ALL types of firearms was settled in favor of AUTOLOADERS a LONG time ago, so why are people still choosing a pump for combat purposes?
Believe me, there are a LOT of superior designs that function with greater reliability than any pump...same reason we choose an M16 over a bolt gun, or a Glock over a revolver....the autos have been proven time and time again, IN COMBAT to be every bit as reliable and more so, while adding the far superior component of being able to rapidly put accurate fire on target. The action of manually pumping a shotgun induces pronounced muzzle disturbance...and of course a semiauto shotgun NEVER "short strokes" due to "muscle memory!"
Also, many foreign made autos are of superior quality and design yet amazingly affordable. I have a stable of pump guns...and even lever shotguns and doubles, but my "combat" shotgun is a Linberta SA with extended (Remington extension) mag tube. With a 20" barrel it holds a total of 9 rounds, has ghost ring sights, top rail, weights about 7 pounds, has an oversized operating handle, as well as action release. It's gas system is self-regulating, annular ring piston design that transitions from shooting Winchester AA Trap loads to 12 pellet 00 Buck S&B, and Rottweil Brenneke style rifled, non-discarding sabot slugs....as fast as one can yank the trigger! The autoloading action takes a LOT of kick out of the gun and makes it actually FUN to blast away with the heaviest loads....rifled slugs group into a few inches at 50 yards firing offhand.
And yes, I know Remington and Mossberg both also make excellent autos....my favorite from that stable would be the Mossy 935 3.5 inch magnum chamber stoked with Lightfield Commander 1-3/8 ounce slugs pushing over 4,700 lb-ft of KE....but of course that's a bit of overkill considering a 2-3/4" 1-1/8 slug is ample medicine for human predators and of course a tubular magazine can carry more of those.
And I haven't even touched on the Saiga design which also has a proven track record with the advantage of detachable box/drum mags.
I was 30 once, many, many years ago. 
