There isn't really a "correct" crew skill for a class, some might be marginally more effective but not enough to worry about. For example Doing synthweaving on an agent may be a bit of a poor match up but chances are you can craft and sell gear to make enough money that you could buy your gunsand barrels anyway .
The drops and commendations are good enough while leveling that you won't need to do much self outfitting but personally I think it's fun to make may own gear so I have alts doing all crew skills anyway. Which class doing which isn'ta concern .
The only thing I'd avoid with the agent is synthweaving because you can't use the gear directly (but Vector can) still I make enough money on synthweaving that I could buy all I need so whatever. Any other crew skill is at least partially useful.