Im in agreement with
@Red Leg ..
With modern loadings the 556 outperforms the x39 in just about every way you can imagine... there is a reason the russians and other countries have moved on to 5.45x39 (their version of the 556).. it just makes much better sense in a fighting rifle..
There was a time you could argue "reliability" in favor of the AK.. but that really isnt the case anymore.. I'd challenge anyone to put equal money into an AK and an AR and show me any real difference in reliability.. If youre comparing a DIY $400 AR built in someones garage with cheap parts by a guy that doesnt know what he is doing to a $1500 factory built AK.... MAYBE the AK wins.. but a factory (affordable) AR from S&W, Bushmaster, etc will hold its own against an AK with no problem these days.. the bugs in the platform, the ammunition, the magazines, etc have been worked out for decades..
There was a time you could argue ammo availability and cost in favor of the AK... but thats not really true anymore either.. the AR is the #1 rifle in terms of sales in the US and has been for a long time at this point.. and there are tons of people making low cost ammo for them as a result (to include all of the eastern european manufacturers that have been producing low cost x39 ammo for all of these years with steel cases, etc..
And the AR is simply more versitile.. for $300 you can buy another upper with a different length barrel.. or in a different caliber (hell.. buy one in 7.62x39 if thats your thing.. they make them)... you can build one in about an hour for $400 or less these days.. or buy one new off the rack built for $650 just about anywhere..
And if the whole AK piston driven system is your thing... you can buy piston AR's now.. or even convert your DI AR to piston for about $250 (Alexander Arms makes a great kit for that...)...
Other than owning one just for the sake of owning one (I love an AK.. and carried one on numerous occasions between 2003-2010 on various jobs in Iraq and Afghanistan.. ) I dont see any reason to buy one these days if youre in the market for a home defense (or even offense) rifle... There are better, more affordable, easier to support, options out there in the US...