I just saw this post on reddit.

It seems that if you fill your character inventory so that any Lost Sector rewards will go to the Postmaster, you can just hold on to the exotic engrams and they will change to whatever slot the Lost Sector rotates to the next day.

So you can farm whatever the easiest one is and wait until they all change to whatever gear slot you're looking for drops for.

Assuming Bungie doesn't fix this soon, of course.

If you're talking about Europa, without question it's Bunker E15. It's full of helpful frames! If they don't outright kill the enemies for you, they'll at least distract them so you can pincer them nice and good. They're not invincible, of course(aww) but pretty much every time I've tried it, they've at least gotten all the way to the final room.

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I think the fastest one if you do it right is Veles Labyrinth. It's tricky, but if you get the path and enemy sequences down, you can get consistent 3-4 minute runs.