The venerable J-cradle has become one of the most popular ways to carry a kayak. Carrying the kayak on its side, it takes up less space on the crossbar. Since it's normally mounted near the outside of the towers, it's easier to pick a boat up and light straight up rather than leaning in over the car. Your chiropractor likes this, as does your lumbar region.
J-cradles are available in a more economical fixed J, or a more deluxe folding model. The folding ones make it easier to get in and out of your garage. Nice.