The AK-47, also known as the Kalashnikov, is one of the most recognizable firearms ever produced. Today it is the most widely used assault rifle in the world. This is partially because of the massive number of them that 'disappeared' after the fall of the Soviet Union. What truly makes them so prevalent, however, is a combination of reliability and low production costs.
The AK-47 was originally introduced for service in 1947 to the Soviet Army. It was developed by Mikhail Kalashnikov while in the hospital recovering from a gunshot wound, and submitted to the Soviet Army for a competition to find a new assault rifle. At the time, assault rifles had only recently been invented in Germany during WWII. The AK-47 was designed specifically to withstand the harsh environments of the Soviet front lines.
Since the first AK-47 there have been many different variants. These include the AKS, which featurs a folding metal stock for use by paratroopers. The RPK is another variant, which is an light machine gun with a bipod and longer barrel. The AKM is a refined version that uses a smaller cartridge, and the AK-74 is another, even more refined version.
In airsoft AK variants are extremely popular for a number of reasons. The biggest reason, admittedly, is that they look cool. After the M4 and M16 there are probably more AK replicas out there than any other assault rifle as well. Because of the wood furniture they can be very heavy as well, which is often incorrectly looked at as a sign of quality.
One great example of the sheer number of options one has when buying an AK is the Jing Gong Tactical AK-47. This AK barely resembles the standard gun, with an all black finish and tactical attachments. The full wooden stock is replaced with a collapsible one, there is an RIS rail running along the top of the rifle and a folding vertical grip in front.
The Jing Gong Tactical AK-47 features full metal construction for durability and that wonderful weight. It comes with a 600 round magazine and fires about 410 FPS using .2g BBs. Of course, the gearbox is from Jing Gong, so decent reliability and powerful performance can be expected. Jing Gong is known as the Tokyo Marui of China for good reason.
On the complete opposite end of the spectrum is the CYMA CM052 RPK. This is an RPK model, so it comes standard with a bipod and has an extended barrel for greater accuracy. This gun features full metal construction with real wood furniture.
The CYMA CM052 comes with a 420 round magazine and fires around 420FPS with .2g BBs. This gun is equipped with fully adjustable sights and hopup, which along with the longer barrel help it place accurate groupings. The high FPS helps with the range and once stabilized with the bipod, this gun is a long range beast.
For your standard AK, the TSD Tactical Gen II AK-47 fits the bill perfectly. This gun features full metal construction with real wood furniture, really a must on any AK replica. It fires around 380FPS using .2g BBs and comes with two 600 round magazines. A slightly longer barrel adds to the accuracy without making it unwieldy.