If you want one of the big 3 to go the way of Sega, or want your preferred company to monopolize...

[curl-6]

If one of them absolutely had to go, I'd want it to be Sony.
While I love many of their games, (Uncharted 1 & 2, for example) I don't like their approach to hardware, particularly maintaining a PS1 era controller in this day and age. (Which they will probably keep for the PS4, which would be an absolute joke. Imagine if the Wii-U still used the N64 controller...)