I have a few bags that I use, depending on the situation: Think Tank Retrospective 20 (for around town), F-Stop Guru (for general travel/day hikes), and a DIY jury-rig that consists of one of my 60L packs and a medium or large F-Stop ICU. Sometimes I’ll have a chest mounted case (Lowepro TopLoader Pro 70) that connects to my backpack, but that’s only if I really want to look like a goober.
For the most part, I’m happy with my bags. It took quite a bit of trial and error to narrow down to what I have now, but I feel that they are most beneficial to me for the type of photography I work on most.
If you are looking for a large pack for which you can do some serious hiking/backpacking in and carry your camera gear, it’s best to just get a pack made for backpacking, make sure it’s fit properly for you, and alter it. This way you have a great hiking pack that doubles as a camera bag, not a great camera bag that doubles as a hiking pack (you’ll know what I mean if you’ve ever hiked with a pack that doesn’t fit well).