I am a fan of Think Tank bags. As is true of many photographers, I have had my share, looking for the perfect bag. Right now I am using an Urban Disguise 50V20, but that won't work for you--it is more of a brief case than a backpack. I have also used one of their backpacks--don't have the number handy. The bags are well made, have compartments in the right spots for cards and batteries. Mine came with rain covers inside and also a nice card pouch attached to the bag. My one bit of advice. I tried a Kimba (?) backpack, which supposedly had the advantage of letting you load the bag by unshipping the whole thing, but then allowed you to open the sides to remove individual pieces. That didn't work so well. On that bag, I also went big--that was a mistake. Smaller is always better, but only if you test it before buying it by loading the equipment you will be carrying into it. Unfortunately, that will be more difficult to do now that Calumet has closed its store in our city.
Good luck