Without having the right equipment with you when you are hiking you will make the trip harder and more uncomfortable to you than needed. A big part of your comfort and enjoyment comes from having the right gear and an important part of that gear is your backpack. Choosing the right one allows you to include all the things you need with you without making the back too hard on your back.
Different backs will feel different while you are carrying them. They will have their weight loaded at different parts of your back. This will make some of them to feel lighter even though they might actually be heavier. Often the more expensive ones will fell nicer to carry and thus increase your comfort and reduce your back pains.
Different backpacks are also structured differently. Some of them include a lot of small pockets while some of them are mostly made of large areas where to store larger stuff. You need to choose what you want to take with you at your hikes before actually choosing with hiking backpack to buy. If you have a partner with you it might be wise to buy one backpack with small pockets and one with larger pockets. This allows you to easily take both big and little things with you.
One thing that you should also look at is how large the actual backpack is. Some can carry more stuff but are heavier. If you don’t need a lot of stuff with you it will be wiser to buy a smaller pack so that it won’t be so heavy to carry.
You should buy a pack that is water proofed properly. Other wise you might face a nasty surprise if it starts to rain heavily.