With the DK coms, buy yourself an orange blaster. They are level 16 and you can keep it updated by changing the mods in it (same with your chest). Also, you might want to look into the odd armor items on the equipment comms vendor.
The Hutta coms will just rot, as there's nothing to buy with only 5, nor anything worth the time to farm more comms
I don't know what all you can buy with the fleet coms, but the vendor for them is on the Fleet, pretty close to the speeder vendor. Just do more space missions to get more of those.
An easy way to get coms is to do the daily heroics on the planet. After you get your stuff taken care of, then switch over to your companion. Once again, she could use a better blaster, and the other armor items that are sold by the DK comms vendor.
Pretty much, I use coms to buy armoring, hilts/barrels, mods and enhancements. Other than that, I will just buy stuff to either sell on the GTN, or the odd item I might need to flush out a full set of orange gear.