I am trying both. Some of my characters will craft and outfit everyone more junior, and some will supply and/or sell. I buy materials on GTN when they are less expensive than from the missions. I dunno, I like doing both, and since I do not play PvP, I could never manage to accumulate enough planetary commendations to keep all the blasted adaptable gear armored, modded, barreled, hilted and all that when you go over 6 pieces each char and companion. On one of my characters I am planning to just buy blue items every 2 to 4 levels + pass down from the unused drop offs (since I am forever overlevelled and can't use the items I pick are several levels behind). But either way is exhausting. I am to the point of dreading each level up.
Yeah, this is tough. I've found the best way to keep gear current is to do your FP daily every day and to go back and run old Heroics for the planetary commendations. Running all of the Heroics from Coruscant to Nar Shaddaa you can get 37 commendations and by the time you need these they should be gray to you so it's a quick run through for commendations. As you gray out a planets Heroics you can add them to your commendation runs. Otherwise, I used blue and green loot drops to keep current when comms were in short supply and checked the GTN for cheap mods.
Also, don't forget the mod vendors that sell green mods on each planet. Those mods are good enough for you to level with, especially if you are over leveling planets.