Now that Firebase White is no longer as easily farmed, I bring you an alternative that is just as easy and quick (30-35 minutes per match): Firebase Rio/Reaper/Platinum! .
Ok, so there a couple awesome new characters and some shitty new Collector weapons that you probably want. Not everyone will have saved up millions of credits, so here's an.
UPDATE: I have spent about 5M more credits since this post and have updated results - click here to see them! Ok, I promised to do a little experiment to.
You can never have enough credits to spend on Spectre packs, so here's a list of the easiest and fastest ways to earn credits in online multiplayer with the least.