Whether or not any one agrees with me Ill say this. Youtube is not the best place for quality reviews or information usually.
Personally I would have to side with Amos here and say go with the spring, after getting my G-spec and a friend of mine getting his M700 and going to the range I can say with out a doubt that the spring is more consistant. As far as Im concerned any thing else wrong with the gun can be delt with so long as it shoot the same every time. Im not knocking the gas guns but with what little I have seen the springs tend to do better in the long run.