First, my bias: I prefer to use camera bags that do NOT advertise "expensive camera equipment inside!" So I stay away (mostly) from bags and rucksacks that are identified with camera brands (like Lowepro, Peak Design, etc.).
That said, I did buy a ThinkTank shoulder bag when I used a Nikon D4 with a 600mm zoom. It was incredible. Very comfortable (despite a big body and bigger zoom plus other stuff and a laptop). Well padded. Well designed. I highly recommend ThinkTank--if you decide you don't mind a photo-related tag on your bag.
Third, don't buy a bag or backpack until you try it and see how it rides on you. If you buy it online, make sure you can return it. I've probably purchased or owned over 30 different bags or backpacks. Some were specific to a particular trip/assignment were I used it and then gave it away/sold it. Some specific to particular equipment (like the ThinkTank shoulder bag). But in a lot of cases it looked good or it was a gift and it just didn't work for my purposes. Backpacks (generally speaking) work better for one gender than another (shoulder width, breasts, etc.) depending upon their cut. You might get 20 people who tell you "buy this specific bag--it was perfect for me!" It was perfect for them. Try it and see how it rides on your body, how easily it is to access stuff.