For a first firearm, you must compare the Mossberg 500 vs Remington 870.
In the USA it is easy for people to buy handguns, so they often do for their first gun. Plus they are able to carry it with them if they are in the right state and have the correct permit. But in Canada, pistols and revolvers are more difficult to get. So your first gun should likely be a shotgun.
For my first firearm, I will likely be getting a Mossberg 500, Mossberg 590 (HD military verison of the 500), or a Remington 870. These are such versatile weapons, allowing you to hunt and protect your home from intruders. Load in a 1 oz slug and you can take down a deer. Bird shot will take down birds. Buck shot will take down medium game and two legged rats (i.e. home intruders). Finally, you can have a heck of a lot of fun shooting targets or skeet with a shotgun.
The following videos will help you to decide the eternal battle of Mossberg 500 vs Remington 870. But a couple of the points that I noted were: