I'm going to horn back in here for a minute.
As a guy who grew up hunting, I've found three basic criteria apply to my firearms.
Reliability is the number one priority. A firearm that misfires, is finicky, breaks easily or jams is nothing more than an expensive shovel handle. Remington, Browning, Benelli, and Winchester all produce excellent auto and pump guns that are very common to the market.
Availability. This not only pertains to the gun itself, but parts as well. Purchasing off brands or obsolete guns really limits your ability not only to repair the gun, but upgrade/modify it as well. Gun manufactures like Ithaca made excellent shotguns in there day, but many you find may be old and overused. Finding a stock or firing pin may become a chore not worth the purchase. Same goes for odd brands. Some have little known issues and getting the problem fixed may cost more than the gun is worth.
Cost. This is where the rubber really meets the road. Generally speaking, high end guns tend to be reliable, but paying 1500 bucks for a top of the line Winchester may not be the right choice.
Given that you are just breaking into the sport, I would suggest a low end model that has proven itself. Here is a PARTIAL list of solid shooters that can be had used in pawn shops and private sales. These tend to be reliable, but as with all used merchandise, can still be abused or overused, so a through inspection should be done, preferably with a knowledgeable friend in tow.
Remington 1100 series
Winchester (generally harder to find) 12,13,14 or 1500 or SX series
A little more expensive gun would be the Browning A5. IMO one of the best shotguns ever marketed. Unfortunately, they tend to be a bit more expensive.
Remington 800 series
Mossberg 500 series
Benelli makes a nice pump as well.
Virtually all of these can be had for 120 to 250 clams used (with a couple of notable exceptions, such as the A5). All are reliable if not abused. I prefer to purchase guns that can use interchangeable barrels and screw in chokes. These offer the most versatility, since as you begin to enjoy shooting, you will invariably wind up hunting upland gamebirds, waterfowl, squirrels, turkey's, and perhaps even slugging for deer.