I would create a hack 'n slash franchise exclusive to Microsoft because they need a proper answer to God of War and I feel they would support my game the best with advertising and bundling.
Sony only supports Uncharted nowadays with huge advertisement campaigns and mass bundling (and to lesser extent Gran Turismo with mass bundling) and leaves every other IP to sell itself on quality and word of mouth. I love the freedom Sony offers developers to create whatever they want without comprise evidenced by games like Journey, Flower, Heavy Rain etc, but I want Sony to support their franchises other than bloody Uncharted.
Infamous could be as big as Red Dead Redemption, God of War could be as big or bigger than Gears of War (per game), Killzone/Resistance could potentially be the next Halo with enough support, LittleBigPlanet could be a huge franchise with Sackboy coming close to rivaling Mario, alas none of these games get nearly enough support from Sony, even their second biggest and most critically acclaimed franchise God of War has never had a holiday bundle or mass bundling or a decent marking campaign, it made a name for itself with barely any help from Sony.