If he's in Economy he gets what I call "compromise class."
The front section of economy is configured 3-4-2 but features little legroom.
The rear section is 3-4-3, so is narrower, but the legroom appears to be ~2-3" more.

Whether there is a preference or not, and whether seats can be preassigned, I'll leave to somebody else.
I am also unsure whether when the cabins are refitted, this strange configuration will be retained, or if they will switch to a homogeneous Y section. (I believe the first MD-11s are refitted with lie-flat business seats, or will be by the end of the year, but mine was not).