I have been a long time user o the Lowepro Flipside 500 and Flipside 400 for my general carting around of my gear on local treks and for travelling, well designed backpacks which are comfortable for long treks and hold lots of gear. I like the idea of the opening to your gear being closest to your back so that when you take it off and put it on the ground/seat/table to access your gear it faces you and the part that touches the ground and may get dirty isn't then up against your back. Not only that, but if you leave the belt done up and take your arms out of the shoulder straps, you can swing the bag around your waist and access the gear without the need to take the backpack off. It is a good safety feature when travelling.
However, I stumbled across a new Lowepro backpack for my travels, the ProTactic 450 AW, similar idea to the Flipside 400 and 500 but much more versatile and a much better design, IMO. This is a perfect backpack for travelling as it also has a laptop sleeve whereas the Flipsides do not. Rather than me tell you all about it, check out the Lowepro site and/or the FStoppers review which describes it very well:
I hope this is of some use to those looking for a great travel backpack and take plenty of gear like I do.