[brooksbp]

I have a 15.4" and it's suitable for travel. Though, I'm a huge fan of multiple screens / OS X Spaces (X alternatives).

There's just no way one screen without multiple screen emulation or external monitors will 'feel' right. Need more pixels!

[aston]

My 13.3" has a screen with the same resolution as my older 15.4". Way easier to travel with, though (half as heavy). I think screen size + resolution is the better question.