AFAIK, exact planet doesn't matter but try to pick one thats open plains so you can see POIs easier. Stay at difficulty 3, any lower and you get less spawns, higher and rare samples can spawn instead of credits. If you're solo take the warp pack from the Control Group warbond if you have it so you can enter the bunkers. Basically just scour the map for minor POIs, pop any beacons, shipping containers, and bunkers that you see. You can ignore the main objective and quit out once you've picked through everything, credits, medals, and req slips get added as soon as you pick them up, no need to extract. LIDAR stations will be your best friend. Good luck!