Been in shooting for over 35 years, my kids have just got into bb's so looking for some kit for them. Looking at the JG G36C or an G&G Combat Machine AEG CM16 Carbine not sure which is more reliable ??? easy to fix etc.
Get the GnG. It should be ok FPS wise out of the box, both are reliable, both are good skirmishable weapons, but the JG will probably need a spring downgrade.
as dev said both guns are well recommended so just go with which you/your kids like the look of best. as for jg needing a spring down grade shops would need to do this anyway to make it legal for them to sell so i wouldn tlet that sway you if you like it just ask which ever shop you go to about it