In what order do I need to upgrade parts of an airsoft AEG?

I'm buying a new gun, and want to upgrade it asap. It will either be a JG enhanced M16 DMR or a JG S-System M4 with MOSFET. Which should it be? I know the first upgrades should be hopup+bucking then tightbore barrel, so I plan on buying a Madbull ultimate hopup and Madbull ultimate 6.01 tightbore. What after that and why?