Backpack + Sleeves (Score 5, Insightful)

I'd vote for a regular backpack and use separate sleeves for each of the laptops. That would give you individual padding on the laptops and lots of extra pockets for mice, USB thingys, dongles, power bricks, CDs, swappable drives, etc. If you're going to use the bag exclusively for the laptops, you could even fold up a towel or something to put in the bottom of the bag for extra padding in case of a drop, or just for the average setting the bag down. As a bonus, your bag won't stand out to thieves quite as much as a laptop-specific bag.