"Probably" the Arsenal SGL-31 is the best on the market.
These are built in the Russian Izhmash plant where the AK was originally made and still is.
These are Russian military spec barreled receivers that are imported into the US and converted to full military AK-74 form by Arsenal Inc.
The barrels are full military hard chrome lined.
These are as close as we'll ever get to a real Russian full-auto AK.
Arsenal Inc sells these through many big gun distributors and your local FFL Dealer can order one for you.
K-Var is Arsenal's parts outlet and sells rifles.
Note that with the buying binge, you may have trouble finding one or finding one with the stock color you want. All original Arsenal rifles have synthetic stocks and hand guards, not wood. You can replace the synthetic with wood.
Another good source for AK rifles is Atlantic:
http://www.atlanticfirearms.com/
One note: A number of companies import Russian rifles and convert them here, but as far as I know only Arsenal gets a special barreled action that doesn't have trigger assembly holes in the fear of the receiver.
Izhmash builds these commercial rifles as "Saiga" brand rifles. These have the trigger unit moved back into the rear of the receiver and use a conventional sporting type butt stock.
In order to convert these, the trigger unit has to be moved forward and the holes in the rear are closed with rivets.
You can see these rivets on the lower rear of the receiver.
Only Arsenal gets a special Saiga rifle without the holes in the rear.
This looks more "authentic" without the extra rivets in the receiver.