Best way to earn credits?

The main point about Credits is to manage them carefully...
When you reached Level 50, you start to choose wisely how to spend them.

Your Credit Earnings come from:
- GW (Mainly ): every GW achieved gives you around 450k,
- Daily Quest: that's short, but you'll have some 200k every day,
- Credit Challenge: 250k 3-times a week,
Missions / Cantina are not relevant for earning credits...

Your main needs will be: leveling up, starring up and gearing.

By that statements, my strategy was this:
- leveling toons: your daily earnings through Quest/GW allow you to level up 5 toons until Level 70 without missing one Level Up,
- starring toons: your Credit Challenge will give you the credits to star up your 5 main toons,
- gearing toons: Missions / cantinas give you the credits needed.
After level 60+, it will take 2 days at least (3 on the last levels) to level up.
So, you will be able to level up some others toons on that days.

With this plan, you will have the credits necessary to reach Level 70 with 5 toons Lvl 70 and 7* (if you can grind the shards).
And probably a good bench, but 5 level below your main teams.