MurrayNevada, let this thread run awhile, and see what you turn up.
My guess, ultimately, is that many, if not most folks will suggest to you that a Remington 870 in 12 gauge is the most common, most readily modified, and most reliable shotgun for this purpose. Some folks use #6 or #7 birdshot for the first two rounds, followed by 00 or #1 buckshot (#1 has more pellets, so some prefer it). I also keep 2 or 3 slugs on the sidesaddle.
Common accessories include sidesaddles, magazine extensions and foreend lights.
Also, see
http://www.vangcomp.com .
Finally, once you get the shotgun, take a tactical shotgun course. And, if possible, try the gun before you buy - perhaps a friend can take you to the range?
Like Chevy / Ford discussions, there are of course various opinions on such a question, and reasonable folks will differ somewhat on the question.
Consider searching TFL for additional threads on this topic - it is perhaps the most common shotgun discussion.
Good luck. Regards from AZ