Auto-mission.
Actually I went with auto-mission because it takes forever to load the map and I got my team wiped out by a bad spawn. (Shevaar on the balcony with a Plasma Blaster. Snipers couldn't hit over the railing, grenade launcher couldn't get close enough to arc over, cover seemed to do nada.
Some of the maps seem a little weighted against the player. Like the Street map. You'd better have at least two exceptional snipers, or you're in deep trouble. I crashed a UFO and found myself fighting two Shevaar, two Taman, and THREE Hovernets. Fortunately the Hovernets go down in one-two shots of the Sniper Rifle. The Machine Gunners I brought were useless. (Plasma Blasters not actual MG's)