I have long wondered what it should be ... Then I decided for the Flipside 500 AW from Lowepro. As a longtime professional photographer, I use a long time backpacks and bags from Lowepro, because they endure a lot and therefore ien reliable "partners" are. The Flipside 500 AW (stands for all-weather) is from the top processing. I consciously decide in favor of this backpack because one comes only from the back side of the equipment and thus offers optimum protection against theft, even if you stand out in a crowd. The front compartment has room for all the useful stuff. However, you would not notice this when someone rangeht since also helps no padlock. The lap belt can be a backpack almost to forward without turning him completely remove if you slipped his arms from the shoulder straps. However, you should definitely stay here one leg placed under the backpack or looking for a suitable tray. Because if the backpack is packed properly, then it will also really hard!
The Flipside offers plenty of space. I stow there 2 large Canon bodys (5D Mark III) with Battery Grip. 1x70-200mm USM / 2.8, 1x 24-70mm USM / 2.8 and 16-35 USM / 2.8. Charger and card reader are also pure and the shoe mount. Ins front compartment can hold extra memory cards, for example, an iPad etc. Macbook Pro 15 "does not fit. I knew however before. No problem.
All in all a super photo backpack for the highest standards, which is worth every penny!