Resolution. I've been buying 1920x1200 15" laptops for along time. My latest laptop is a retina MBP, which I have only because of the resolution (it's fine otherwise too, but nothing special). I just wish the screen wasn't glossy.

Other requirements: SSD, discrete Nvidia graphics card (which do great under Linux), lots of RAM.

I probably wouldn't work anywhere that wouldn't let me run Linux on my machine without virtualization.