I carry a 3rd bag for 15" MacBook Pro. Messenger type bag with shoulder strap. Its cumbersome and looks pretty busy I think. Plus it always swings infront of my waist so I'm always readjusting it to go around the terminal.

It sucks, but im too scared to put it in the hands of rampers when i comute (by putting it in my overnight bag). I've though about putting the computer inside my overnight bag, like in the center- surrounded by clothes. But going through security wouldnt be fun, so the 3rd bag works for me. Just basic black leather.