I was in the same position, and came to the conclusion that it all depends on what you'll do with the machine. The 13" is good for internet browsing, music, and light photo/video editing. The 15" is better for things like Photoshop, Aperture, and Final Cut. (The serious stuff) Where as the 13" will feel cluttered. When I was deciding the price difference of the 13" and 15" was much more. I decided on the 13" and eventually got a monitor to use the majority of the time; however, I'd be okay using the 13" screen 95% of the time if I didn't have a monitor.