If a person had to choose only 1 method of oral hygiene, what would be the most effective for achieve health gums and teeth: 1- brushing with toothpaste 2- flossing 3- rinsing with mouth wash
From a medical/dental standpoint, flossing and brushing with or without toothpaste is the best way of eliminating plaque, which can cause cavities and gum disease.
For the philosophical aspect of your question: If you had to chose between the two (and you should be doing both!), I would floss, since floss reaches more easily between the teeth than the toothbrush, while being able to remove plaque on the surfaces of the tooth which the tooth brush can reach.
Mouthwashes are not useful without prior mechanical removal of plaque.
It should be noted that your question was already somewhat answered in another post: Is brushing teeth without toothpaste actually harmful?