Let's rank the developers at Microsoft Game Studios. To make this interesting, I'll include past and disbanded studios that ever released a game on the Xbox 360. Let's try to keep this in perspective, so only rank them based on what they've done on this one console (that really only applies to Rare and Ensemble).

So the list looks like:

Lionhead (Fable II)

Rare (Viva Pinata series,  Banjo Kazooie: N&B, Kameo, Perfect Dark Zero)

Turn 10 (Forza 2)

Bungie (Halo series)

Ensemble (Halo Wars)

So my rankings are:

1. Bungie

2. Lionhead

3. Turn 10

4. Rare

5. Ensemble (I liked Halo Wars, but hey, it's got some tough competition here)

1. Bungie

2. Turn 10

3. Ensemble

4. Lionhead

5. Rare

Bungie and Ensemble are no longer firstparty.

So the list is
Rare
Bungie
Lionhead
Turn 10

Bungie
Ensemble
Lionhead
Rare
Turn 10

Rare
Lionhead
Turn 10
XBox Live Productions
Wingnut Interactive(yet to release a game)
BigPark(yet to release a game for them)
343 Industries(yet to release a game)

Lol, I saw that after I posted. I tryed to edit it but I lost my connection

And Bizarre Creations was never first party

They developed the Club as well as Blur. They are owned by Activision now

Rare
Lionhead
Turn 10

If you can still count Bungie, then they'd be number 1.

Aren't all of these studios 2nd party anyway? The definition confuses me sometimes....