It's a shame that 14" shotguns are considered NFA or whatever you call you 200 tax stamp thing you have to apply for with short shotties/rifles and suppressors in the USA. The Mossberg 590 14" is my primary shotgun, and with the 4 round speed stock and side saddle, I can run with 15 rounds on the gun itself, and still have something short and maneuverable for fighting inside buildings and structures. The slightly longer 590 is still a pretty amazing tool, as of course is any 870, but try and get the actual Police variant, and not the cheapy express if you can afford it. Honestly for the money I would say the 590 full length is my personal favorite, a 9 shot shotgun with excellent factory ghost ring sights, and a 4 round speed stock. You can run 19 rounds on that shotgun with a side saddle as well.
The only downside is Mossberg 590's are a bit of a pain to break down and reassemble for cleaning, the 870 is far, far easier in this regard, and the 590 in comparison is like some sick twisted IQ test on spatial orientation.