I'd recommend a G36 model. I've handled the C and K models myself, both a Classic Army and Jing Gong (early gen) versions. They have the rails you need included, and fully railed handguards are around. The take-down is simple and you don't have to tear out all the internals to swap out a hop-up or barrel or even the mag well. Due to the design, its rock solid without wobbles. The only thing that will be a mark against it according to your 'wants' is the full metal obviously. The v.3 mechbox makes up for that, in my opinion. A lot of people would call it the best type and I agree.