Alpha Site seems to be the popular choice. My squad did it on Lost Platoon. Key hints -
You need one driver and one gunner for the Warthog. The Warthog is the key and will do a majority of the troop clearing. The driver needs to always keep on the move, and always keep a distance. Losing the Warthog will hurt you very much until you get a new one at the end of the round.
One person in our squad would hold the Spartan Laser. This can be found on the bottom floor room to the right of the Warthog spawn.
The 4th person had a Chopper whenever possible, to assist the Warthog. Splatters work well in most situations.
Our fight was centered in the field where the bonus ship shows up, and the hill that you come down from when playing this level in campaign. At the beginning of a wave, the Spartan Laser player and the Warthog would sit up at the entrance plateau when not gathering weapons or health. The Laser player can hang back and the Warthog would drive in a tight circle (use the circle on the ground for a good guide, stay to the outside of it) to attract the gunship fire but still not directly take much of it.
If a Wraith is dropped in either of it's two spots, it can easily be taken out by a Laser from the entrance plateau.
Choppers are to be horded. If ever at all possible, try to kill the driver but save the Chopper. We had a stash of spare Choppers up on the entrance plateau for most of the game.
Warthog also should be used to transport Laser player back and forth from central structure for restocking, and to protect the Laser player during bug attacks.
Tough parts to look out for - on respawn, a player will often spawn inside one of the dark garages, with enemies hanging outside of it. If not done carefully, this can lead to a lot of lives lost quickly due to spawnkillings. Have a vehicle or surviving teammate make a distraction. The trapped teammate should NOT FIRE on the enemies, and make an effort to escape the garage.
Note - we also had a very rough situation where 3-5 brutes actually left the fight and camped the middle structure's top floor. We did not know this, and the Warthog was almost destroyed with a Fuel Rod when we tried to pickup some health. We had to sit on the entrance plateau with Chopper/Warthog shooting randomly into the building to clear them out.
Note 2 - This takes a LONG TIME. 3 hours for us. We did not know this would be the case. Please make sure you are rested, have used the bathroom, have eaten, and have a beverage near you to minimize discomfort. We would have probably kept going, but we let ourselves get killed on Set 5, Round 1, Wave 1 just so we could eat and use the bathroom.
Note 3 - Added Dec 20 -
For S&G's, here's a link to the game. http://www.bungie.net/Stats/ODSTg.aspx?gameid=4158192&pl...
We weren't anticipating actually getting the achievement on this go, and figured out strategy as we went.
Six El Sid (me) drove the Warthog and Butterdumpster gunned. As you can see, I have only 68 kills while everyone else has at least 425, as my main job was keeping the Warthog alive. I actually got the achievement for not killing anything in a round accidentally this game.
JohnMcLain8739 was the sniper/lazer main on the hill.
Bitteralmonds was on a Chopper whenever we had one. He actually splattered a large majority of his kills. He DID have the most deaths by far, but to be fair, a lot of it was him getting spawnkilled in the dark garages. You gotta watch out for that.