Well, I am not quite sure, what are MS first party except Halo that are currently out (and I am not even sure that's made by MS, I thought it was made by Bungie, and development of it started before the purchased I think) , so I would go with Sony.
How has MS's acquisition of Bungie harmed the company in any way? It has only assured their financial stability, and vastly increased the rescources at their disposal. Being the developer of the #1 selling Xbox game has only given them the industry-wide recognition they've deserved (and been denied) for the past 10 years. I'm crying.
And as a openly-biased Bungie fan since 1997, I say this with the utmost confidence: