I own a Remington 870 Marine Magnum and a Mossberg M590-A1 14" and they both KICK-ASS. I dont know what to tell you...try them both out if you can.
The Mossy 590 has a fatter grip on the stock and rifled sights (Ghost sights) which are very accurate and can be adjusted for windage/elevation with a black rear and a highly visible "red-ramp" (Orange) front sight blade.
The Remmy 870 generally has a front bead sight, action smooth as a babies bottom, easier to clean/fieldstrip
Mossberg 590A1 20" ...........9-SHOT capacity
Remington 870 18"..............6-7 SHOT capacity
Both KICK-ASS!