Great advice on here already. My add is : 1) find out how much the backpack weighs when empty; 2) think really hard about how you like to travel; 3) consider water resistant fabric.
I have a G4Free with a cinchtop. Love it but they dont make that version anymore. I love its simplicity & durability but it doesn’t open clamshell. I like clamshell so I can see & access everything easily. You may also want to consider how you like to travel & what reduces your stress when traveling. For me its being super organized, easy access & ultra lightweight.
I got a Pakt travel backpack to accommodate my clamshell preference. I LOVE the organization & access of my Pakt but it weighs 4 pounds empty which is way too much in my opinion. And the shoulder straps are a bit thick for my frame. So, I use it for local travel but not international or any trip where I think I may have to walk a long way with it at full weight.
Pakt has just come out with a new, much lighter pack but you may only like if if you’re an ultralight packer. Worth checking out though.
Good luck! Would love to hear what you decided on.