Ah.. you mean adaptability to making it an airgun. Well heres my take on the subject
If you're open minded you will see the M16 has a clear advantage in this field. The barrel is in line with the stock so you can mount the air tank directly behind the valve as opposed on the AK47 where you need a couple of knees to get the job done. Less parts = less weight, another advantage to the M16.
Also, the AK47, above the barrel has a DI (direct impingement) gas operating system witch raises the optics further away from the barrel witch interferes with aiming at different ranges at the same time and makes a lot of unused space in the wood if you're trying to make a replica. If you go with high pressure and high volume and maybe a heavier projectile, the M16 has the advantage of the barrel and stock being in line so you have more control over the weapon. Also, the pistol grip of the AK47 doesnt look very ergonomic... not something I'd like to hold for long periods of time. It even requires a special attachment for weaver or picatinny rails so you can mount optics.
The Ak47s looks are more liked simply because its acknowledged to be robust and simple to use. Ideal for a rookie, dont clean it or anything and it will go bang. However, you cant say the same for the airgun version.
On the other hand, the M16 had a lot of controversy with it failing and so on. This was only because the soldiers werent taking care of it.. take care of your equipment and your equipment will take care of you.
Many guys with AK47s like insurgents in Iraq dont have any other equipment other then their weapon and maybe a canteen so obviously they dont follow that rule and therefor, the Ak47 is ideal for them.
Dont be fooled... every firearm has to be cleaned even if its not DI or not even using gunpowder as propellant.
All in all, I dont think either are best for use in airgun replicas but if I had to pick one, it would be the M16 because of its obvious advantages.
