I have lots of backpacks including a number of photo backpacks. My problem with photo backpacks, they are not comfortable. They have great interiors, but the harness, is terrible, and if you pack heavy, it will kill your back. I do use the sling bags, which are very small bags that you can carry on your back. So what is my advice for packs? Find a pack you like, one that fits, with zippers that will open the entire bag and customize for camera equipment. The key is finding one that fits! If you go backpacking and buy a pack, they spend the majority of the time getting the right fit. You should do the same thing with your potential camera bag. So, how do you customize? You can get inserts, wrap lenses in bubble wrap, get lens coats, all protect your equipment. You can get a pack cover to protect from rain, and always carry trash bags for extra help. Use the small nylon bags for small essentials, and ziploc bags for memory cards. That way, when you unpack, you have the gear in a bag(s) for storage. Loading the pack is like packing luggage, you need to think about what you will need and when. I keep manuals, memory cards, lens cleaning materials in the top lid which usually has a zipper compartment. I attach light jackets, tripod to the outside. With a first class harness for carry, a tripod on the outside is not difficult. AND, the harness is made to carry the load. I also suggest you pack up at least some of the stuff and take it with you to REI or where ever you buy your pack, and try it out. What's important, the fit of the pack. Second reason to customize the pack, you will figure just how much weight is comfortable, and select equipment accordingly. You can likely afford a couple of professional backpacks for the price of one photopack. That's especially true if you plan and shop for your pack at the end of the season when prices are reduced.
Now all of this discussion is for packs carried on your back with the intention of walking some distance over terrain where wheels will not work. If you intend on traveling on a surface that allows wheels, by all means get a rolling camera bag. Here, I like camera bags, their organization works for me. My favorite is a pelican with wheels and dividers, which work to carry a ton of gear. Caution, if you are flying, you should consider lighter weight alternatives like ballistic nylon bags with wheels since weight is a factor in today's air travel. Delsey has a nice bag with wheels in this category, but other brands are likely just as good. The nice thing about camera bags with wheels, you can pull out the dividers, and use the bag as regular luggage or a combination.
A third alternative for travel which many use is a good camera vest. I have written about camera vests on several occasions, but they hold a lot of gear, work well. If you fill one up when traveling, you look a bit weird with all that "stuff" in your pockets. The upside, the person next to you will not likely want to bother you with conversation.
What made me thing of all this, I just received my vest from Vested interest, I'm traveling to DC this weekend, and I just ordered a pack from Mystery Ranch for my son's birthday. He and I talked about using the pack for photography. He climbed a 14,000 foot peak on Tuesday and intends on doing more with camera gear. I should have written an article about needing oxygen when I hike!