Alright, now I am headed into two great debates here with this one. Which is better? Mossberg or Remington? 12 or 20 gauge?
Let's start with the first. My stance on this is, there is a serious trade off either way you go, you will get a quality shotgun. The Mossberg 500 has a receiver made from aluminum, as where the Remington has one made of steel. Some say steel is better for this, but there is no real evidence that the aluminum has any problem staying put together. Steel is heavier, therefore the Remington's receiver may absorb more of the recoil, however the Aluminum Mossberg will be lighter and easier to carry.
The Remington does not come drilled and tapped for a sight rail like the Mossberg does. One thing I like about the Mossberg, is the safety is located on the top of the receiver. This makes it real easy to access with your thumb when in firing position. The problem with this is, if you install any kind of tactical or pistol grip stock, you will need to let go of the gun to disengage the safety. So that feature has its ups and downs as well. The Mossberg comes at a more competitive price and commonly at Big Five comes with both a long barrel with threads for a choke tube and a short barrel for home security. Mossberg's accessories are just as abundant as Remington's and sometimes more affordable.
Downside to Mossberg is that, it has absolutely no recoil reducing features unless you get them after market, Remington is a little more dolled up and has more of these features.
I don't think that either of these guns are any better than the other I just believe they have their trade offs.
The 12 and 20 gauge debate!!
12 gauge has reigned the market for generations on end, right fully so. It has the power to take anything down, and ammo is available in every variation. But that being said, with toady's advancements on rapid burning propellant (gun powder) and wads that fully encase the shot shell, the 20 gauge will now do anything the 12 did before, and with less recoil and weight.
How is this possible? The 12 gauge has had the same advancements! Yes this is true, however, the 12 gauge didn't need it. I never noticed the transition when it comes to the 12. I did notice them when I shot a 20 gauge and blew up a coconut (which has the same density as the human skull).
The 12 gauge always has been and still is "the bad ass gun" but I am here to say that there is no shame in carrying a 20 gauge. I want to see anyone shoot a 12 gauge with a cheap narrow pistol grip at some ballistics gel and do the same with a 20 gauge and see which they would rather shoot in an improvised situation such as being woken up in the middle of the night and shooting one handed trying to round up your kids with the other hand.
Ultimately when it comes to shot shell, You have the same size pellets with both guns, and you have the same velocity with both guns. So when it comes to shooting in a field or in your house, I don't see any real need in the extra power of the 12 gauge.
Now hunting in wooded areas, now that may be different. You may want the more pellets that the 12 gauge has to offer, I still think any hunter worth his salt can get the job done with a 20, but I could see noticing an improvement with the 12 gauge when your shooting at a turkey through tree branches.
All in all it is up to the shooter, but don't rule out the 20 gauge, A coroner can not tell the difference between the wounds.