The first thing to consider when choosing a backpack is size. You may be tempted to buy a big backpack: maybe 50-80 liters. This is almost certainly what you want. Would you like to think about packing as little as possible, certainly less than 15kg in the package. The best backpack for travel is probably 30-40 liters, which allows everything you need and prevents you from packing extra-terrestrial stuff that you will use and hurt your back.
The best backpack for travel will also be lightweight. Surprisingly, many cable harnesses and materials are unnecessarily heavy. You must take into account the durability of the material for the type of use it is likely to make. Some ultralight materials can be very durable but will tear when worn in the airport's conveyor belt. If you fly often, you are thinking of harder material.
The best backpack for travel can be locked. If you have a mountain-top tiling bag, it's unlikely that it will be easily locked. You may need another "cover" to cover and lock it for flights, luggage, and leave it in your hostel or hotel room.
The size and shape of the backpack is probably the most important factor. There is no amount of reading that can help you with this: you have to try a bag with some weight in it and get help from a friend or business staff to fit properly. You may find that the harness sits directly on your hips or around your chest. The length is too long or too short – it creates pressure in the wrong places.
At the end of the day, the world's finest travel backpack is a personal decision, but you can learn a lot of reading travel blogs and ask people who have long been traveling. There are many people willing to help with your travel plans.