Stacey has it down pat:) I would definitely recommend getting a pack with those three features (a zipper cover to cover the straps, an attachable daypack and a suitcase style opening).
As for brands, having worked in a sports store for over four years, and my partner is a manager of one, I can say that BlackWolf is definitely a good brand to go with. Having said that, I have never personally bought and used one or a Kathmandu one, but I have never heard of any faulty ones. Caribee in my opinion is a category below in quality to BlackWolf. I’m sure that like anything, you get what you pay for, so I would assume Kathmandu brand bags would be better in quality than BlackWolf. But if you are not prepared to fork out the money for one, BlackWolf is certainly a great option.
My partner and I are taking the Cancun 70Lt and Cuba 75Lt BlackWolf packs on our 36 day tour. There are various ‘models’ within the BlackWolf range, basically the more you pay the more features there are (eg the Cuba has padlocks and a rain cover, whereas the Cancun does not).
Hope this helps!! I know it can be confusing with so many people offering their opinions, but when in doubt, work out what your budget is, do your research, and ask shop assistants for help