Perhaps you've noticed antique quilts in museums with a very visible centre fold line. The eye picks up that middle crease very easily.
The best way to store your quilts is to fold them in thirds avoiding that centre crease.
If you want to be extra cautious, you can roll up a piece of fabric and place it in the fold then fold your quilt over that tubular barrier. That will help avoid a visible crease.
Some collectors like to lay their quilts on a guest bed and have them flat. The quilts are just piled up one over the other. I think that makes them more difficult to access but at least they lay flat.
Another interesting way is to roll them. I use a pool noodle as my centre support. I use this method for my textile art work.
For the quilts that are in use, I fold them in thirds then roll them into a large cylinder shape. They stand upright in a basket near the couch readily available! Love to see all the colours!!