With the new MacBooks around the corner, I'm torn between the 13" and 15" (or more likely, 14" and 16") versions. All things besides size and weight equal, what notebook screen size do you prefer and why? Doesn't have to be MacBooks of course, I'm interested in all thoughts on this topic, especially from people who tried both.

I can't decide whether being on the move often is an argument for the smaller version (lighter), or the bigger one (more comfortable to work without an external monitor).