Why are you asking for advice when you refuse to take any?
Okay so I'm back and this time with a (hopefully) better question. This time I decided it would be between the G&G M4 Carbine with plastic lower and the King Arms "cansoft" M4A1, it's not really cansoft because it's full metal but the hand grip, stock and fore grip are clear plastic.
You also didn't ask a question, are you looking for justification of your low-budgeted choice?
Also, G&G has a metal gearbox casing. There you go.