I'm not sure there'll ever be 100% agreement on this topic!

For my part, I'd go two window seats one behind the other. Here's why:

• both pax have access to control window shades (can be useful to control glare on TV screens). You lose that functionality in the centre of the plane
• the seats feel more spacious and more private on the sides. The middle seats can feel a bit confined, you have no window view and little sense of privacy
• two windows mean both pax are sharing the same aisle (board together, deplane together, not separated by the solid partition running down the middle of the cabin)
• the centre seats are not all that conducive to holding a converstion. And for the amount of conversation you might be able to achieve you might as well sit one behind the other and stand up to talk.
• the loudness to conduct a conversation across the centre of the plane is probably going to draw the attention of other pax sitting around you

For two windows you trade about 5 minutes of talk time in the centre seats, and you gain window views, shade control, more sense of space, greater feeling of privacy.

Others will have a different take.