Saiga is an AK variant made by Russian American Armory. Available in .223, 7.62x39, .308, .410, 20ga, & 12ga. From the factory they have been "sporterized". Meaning the trigger group is moved farther back on the reciever and they are fitted with a classic rifle style stock. They are easily converted back into typical AK form with a stock and pistol grip. I have the x39 and it's rock solid. These are purely defensive firearms in my mind. Though you could hypothetically hunt with them, there are better options. The AK platform is durable, reliable, easy to maintain. Google Saiga and you'll find far more than you ever wanted to know.
They are bad ass, but a shotgun in more traditional form gives you a little more versatility with the ability to change barrels. Being a better design for hunting or shooting sports while still being a viable defensive firearm. Beyond that the main functional difference is that Saigas have a detachable mag vs. a fixed tube mag. Each has it's advantage. If all you want out of this firearm is fun or crowd control, then the Saiga is awesome. If you want a little more versatility like hunting or skeet, then a good tube fed auto would be favorable.
A little update....the Saiga guns are made in the same factory the original AK47's were made, by ISHMASH. They were distributed in this country by Russian American Armory, but are nowadays more apt to show the name Legion, and the RAA has been scrubbed out (a velcro like space on the receiver).
While the guns are outstanding in their sporter imported state, lots of folks end up converting/restoring them to their original configuration or some reasonable facsimile thereof.
I have both a pair of 7.62x39's and a pair of Saiga 12's. I've converted both rifles, and one of the shotguns. There are advantages to the conversion. For around a hundred bucks, or a bit over depending upon your preference, you get your choice of pistol grip (as opposed to the light and 'cheap' factory 'sporter' stock), you remove the trigger transfer bar required for the importation, and replace it with a smooth, high quality trigger set, you can use whatever type and size of magazine, both foreign and domestic, and it's legal...and anyone with any kind of mechanical aptitude at all can do the conversion.
Now I also have some Benelli semi-autos, and some pumps, and I'm ashamed that they spend virtually all their time in the safe. For the Saigas are so doggoned much fun, and carry so much firepower (via 20 round drums), that there simply isn't enough time in the day or week to waste shooting other shotguns...blasphemy I know, but those who shout that, probably haven't tried the Saigas (or else have some sort of personality disorder).
And finally, the really high prices of the past few months have just very recently come down to a much more reasonable less than six hundred bucks.
but keep in mind when going the shotgun route ---> IMO in a survival situation one of the benefits of most pump and SA shotguns is the fixed magazine tube... if your on your feet in a survival situation it is easier to carry less weight/bulk (ie... less mags), and its very hard to lose a fixed tubular magazine as a opposed to a detachable mag (saiga).
The 12 rnd mag for the saiga is too much bulk, and the 8 and 10 rnd mags dont offer much more capacity than any standard 20" pump or SA.
Ive got 2 saiga 223's and 1 saiga 5.45 (7.62 is illegal also in my state) all converted. Comparing the same scenario for rifles is apples to oranges, as the detachable mags for these rifles are invaluable considering they hold 30 rnds (most popular) compared to a much lower capacity for a fixed mag rifle. For that im willing to sacrifice the extra bulk/weight.
For fun, id love to have a saiga 12 ---> if i didnt live in a restricted state that bans the ideal configuration on a saiga 12 (pistol grip) i would have one. When all hell breaks loose, ill be carrying my mossberg, if i decide to carry a shotgun at all.