What’s the best travel bag? Easy answer: there is no best travel bag.
Get any backpack that’s small and comfortable on your shoulders.
That’s it. Other than that, the bag is irrelevant when you pack light.
The importance of the “niceness” of your travel bag is directly proportional to the amount of junk you pack. Pack 60 pounds of clothes, jewelry, electronics, and other unnecessary nonsense, and you’ll need expensive sturdy luggage to keep it all secure. If you pack super light like I do and take only the essentials, the specific type of bag becomes much less important.
I’ve traveled with everything ranging from a nice, name brand, well-constructed backpack (currently a Patagonia sack that cost me about a hundred bucks) to a disposable drawstring plastic shopping bag from The Gap. Yeah. You read that right.
Most of you likely already own something in between the two extremes. Everyone’s got a backpack sitting in the back of the closet somewhere. So start with whatever you have; it’s probably good enough.

What you do not want to do is go out and buy a brand new bag without first working on all the other, vastly more important stuff that will allow you to travel lightly. The type of backpack you have is the least important part of traveling with minimal volume & mass, so if you do plan on upgrading your luggage, wait until you’ve addressed everything else first.

The specific bag is really not that critical. Since we’re not taking much stuff anyway, our bag will be relatively light, so even a very simple Jansport pack like what’s pictured above will do just fine. When I was poor and in debt from years of student loans, I didn’t want to spend a hundred bucks on a fancy-pants bag, so I just used what I had. It wasn’t quite as comfortable as what I carry around now, but it still worked fine and did not limit my lite travels in any way.
I will say that the Patagonia Refugio pack I use now (pictured earlier) is super comfortable and well made. Patagonia makes solid products, so I expect it to last for at least a decade before it needs replacing.
I prefer soft, frameless backpacks to carry-on sized roller bags because they’re easier to carry around and easier to stash on planes when the overhead bins start filling up. There are some rare situations where I’ll travel with a roller bag; usually when I’m going to a work-related conference and I have to pack a suit.
But when I’m traveling for leisure? Nah. It’s too big, and I don’t need the space.