Depending on your kid’s age they tend to like things that are “trendy” and “in-style” but most of those are very expensive and, truth be told, not made of very strong stuff. You’ll have to come to a common ground with your kid and try to find one they like, but that’s also not going to make you cry as you open your wallet.
This may take time, but you’ll just have to search and search in the right places, keep your eye out for sales, low prices, etc. Just know that it may take some determination to find the best backpack for your kid.
OR, you can just go online to a trusted resource to find the best–erhem, read High Sierra here–that’s my opinion. Just check out the awesomeness–that’s actually kind of the easiest route. Heh.