CSG seems to have less random spread pattern and more consistent damage, most likely due to higher pellet count. Furthermore it's got tighter spread too so CSG is the winner for me.
JG is moddable, but mods matter little in these two guns. Best setup is probably mag pull + 3 point sling which Country Gent offers anyway. People preach about IR but you're probably better off swapping to your secondary at the range it becomes relevant. Sure you can put cj3 on JG but the spread becomes horrible, so why not just play NFAS as it has same spread as JG but faster TTK?