Value to cost ratio simply not good enough on any of them in my opinion. Just because manufacturers make internals/externals out of chocolate and they don't bother with QC it doesn't mean that I should fix their product with my own money and free time.
This question was asked before and my answer is the same again: buy a Marui NGRS MP5, which is as realistic as an GBB can get without gas, and the build quality is one of the best if not the best at the moment.