I prefer backpacks as go bags because they leave your hands free, and are easy to carry. The easy to carry part is the most important. Some shoulder straps are made with padding and anti-slip materials. This allows you to walk comfortably with a heavier load than you could manage with another type of go bag.
Having your hands free will make it easier to deal with potential problems. Not having to carry something in your hands will make it easier for you to walk. You can also walk faster. If you need to evacuate in a hurry, that could be essential to saving your life.
Empty hands means that you will be better able to deal with a problem as it arises. One of these could be encountering a large vicious dog. It is common for animals to be roaming around loose in disasters, so this one is fairly likely. You might like to have your hands free to hold a big stick or something to keep a vicious dog away until you get to safety.
I can say from experience that if you carry something to hold off a big vicious dog, you had better be able to use it. The dog may be very quick and agile and bite the stick and rip it out of your hands if you are not ready for that. Your attempts to hold off a large vicious dog are likely to cause it to be annoyed. This can result in a more vicious attack. Practice is good. I don't mean beat up a dog. I mean practice wielding the stick.
Obstacles in roadways and on sidewalks are a frequent occurrence in many disasters. It could be very helpful to have your hands available to get over or around obstacles.
Backpacks are not all created equal. Some will work better for an individual than another. One of my problems with backpacks is that I am smaller and therefore have smaller shoulders than average. This means many backpack straps slide down my shoulders as I walk. This would not be good when you are trying to hurry. It could also make you tired and less able to cope with obstacles and problems.
Some backpacks have internal frames and some have external frames. The external frames will generally allow for heavier loads. Both internal frames and external frames can have waist belts. If you are carrying a heavy load, waist belts will make a tremendous difference in your ability to walk well and not get tired.
There are some very fancy and ingenious systems to make backpacks easier to carry. Some really work very well and allow you to balance part of your load on your hips through a kind of harness and a couple of belts. It is possible to carry more than your own weight with one of these and not get a sore back and shoulders. I have done this. Just don't lean over.
Backpack stores and sporting goods stores often have knowledgeable employees who will help you find a backpack that is suited to you and your specific needs. You can learn what you need to know about backpacks, but it will take time and work to do it.
It might be worthwhile to go to the experts for help, even though their backpacks may cost more. They will probably work better for you. One problem with this is that wonderful backpacks that allow your heavy load to float upon your back and hips tend to be pricey. You will have to become informed enough to know what options you are willing and able to afford.
An option that I like in backpacks is a bottom dump feature. It allows you to load from the top and unload from the bottom. This really speeds things up when you are packing and unpacking. It may not be as wonderful if you want only one small item.
Some backpacks have a day pack that is detachable. That allows you to park the heaviest part of the load in a safe place and still have a small light backpack to carry around. When attached to the main backpack, the day pack functions as a large pocket.
I believe backpacks that have easily accessible water carriers are very important. They allow you to drink as you walk. Some even have an arrangement called a hydration pack. It is a refillable water bag that includes a small hose and a clip to hold a bite valve near your mouth. This is the best to keep you from becoming dehydrated, but may be unnecessary expense and overkill if you only have to walk a short ways to transport or a shelter.
If you have a family, it would increase your familys' chances of survival and comfort for each family member to carry some water and drink frequently. A disaster is not the time or place to become ill through dehydration.
If you have very small children you may want to make special arrangements to carry them or give them a ride. Some of these might be backpacks especially made to carry children, jogging strollers, and bicycle trailers for children to ride in.
Whatever you choose, you need to know how to use it and practice using it.