The bike handles way better with the weight low and as close to the center of the hub axles as possible. If you are traveling super light you can get away with strapping stuff to the top of the rack, but I haven't found this setup to work well for self supported camping and touring. With a tent, sleeping bag, sleeping pad, stove, fuel, tools, rainclothes and some food and water the weight adds up fast, even with ultra light gear.

That being said, you should go on some test rides with what you have once you get your bike, and see how it goes. You'll need racks with either setup, you can always buy panniers later on if you want them.