Upgrading the hop up
I currently have a G&P m4 carbine. My hop up broke so I'm looking to go ahead and upgrade the hole unit. Question is, what's the best hop up unit? I know a metal one piece unit is a good place to start... Thank you in advance.
P.s I realize this should probably be in the upgrades and modification section but I figured were talking about the simple hop up unit so it's in here instead.