We are using the keyhole style because 1. It's beautiful! I just love the look of them. 2. It's practical. According to Gaia's Garden, Second Edition: A Guide To Home-Scale Permaculture,"If we wrap a typical 4 by 15 foot raised bed unto a U shape with a small central opening for a path, we cut the path down from about 22 square feet to 6 square feet. Less than a quarter of the ground is surrendered to paths." Less path space = more plant growing space.
You can reach all sides of the garden from the keyhole path or the outside of the garden beds. As suggested by Permaculture design, you can place the low growing plants you wish to harvest often closest to the path(say lettuce) and the taller plants that you harvest less often (say corn), near the back. Viola!