Realistically, what is the biggest franchise that Microsoft can buy out that would give them first place in console sales?

[Nuvendil]

Purchasing a franchise would be a bad move. MS has repaired their image quite a bit, but they are still under scrutiny. Purchasing anything of size would cause a *lot* of backdraft that could damage them and the franchise purchased. However, all things being equal, diversification is what they need. So I would actually say The Elder Scrolls. It's a franchise still growing and different from their current lineup. However, as I said, purchase is unwise. Now, investing in creating their *own* franchise of similar style/size/scope/genre/etc would be a wise move.