Most likely with no static ammo pickups for starter weapons on the map, it'll be DMR/Boltshot/Frag Grenade/Regen Field or Thruster/Ammo/Shielding or Mobility.
The fact the DMR is so accurate with reduced bloom means that they will use it to ping headshots across distances and then dominate with the boltshot up close. With the ammo perk, they don't need to resupply anywhere. Thrusters help them strafe away or avoid being overrun or regeneration field automatically starts their shields again. Frag grenade solely because it's more powerful than a plasma grenade which is really nerfed in this game besides sticks. and mobility or shielding because unlimited sprint allows you to quickly traverse distances or gain drops or shielding which allows faster re-gen.