The best ones out on the market are: JG Bar10 - Cheapest, if you don't have a lot of experience upgrading, this gun is relativley simple to upgrade with aftermarket parts. Pretty decent still if left stock. Classic Army M24 - A lot higher build quality than the JG but is a little difficult to upgrade compared to the Bar, still good if left stock.
The externals on this gun are 10x better than the JG. KJW M700 - It is gas so it is different in comparison to the others that are spring. Build on the outside is incredible and is on par with that of the Classic Army.
As you can imagine it is gas so internally it is difficult to upgrade.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.