The method by which you listen to music on the go is a highly personal thing. Headphones have their place and are great for deep bass and sealing out the outside world. Earbuds are lighter, smaller, and often better for listening during physical activity. Chances are you have an arsenal containing both that you break out for your immediate listening need.
But if you had to make a binary choice, which would you go for? Headphones forever or earbuds rule?