Galactic Power Value per credit - mods vs character levels?

Upgrade any available star level all the way to 7*. Then level all characters to 43. Then gear up all characters to partway in G6 (or until gear runs out). Then level all characters to 53. Then gear up all characters to partway in G7 (or until gear runs out). Then level 5-dot mods to 12 for all characters. Then level all characters to 85. Then level all mods to 15.
That's pretty much the easy route to the most efficient use of credits. Not necessarily the best route for everything else in the game, mind you.