I would have to say that overall, distance is tougher and more time consuming. I haven't done much sprint based training, but from what I have, it seems like a very short-lived intense period of difficulty. With distance running, it is a steady stream of suck that lasts for a very long time. But don't take my word for it, or the opinions of anybody else. Try it for yourself! Go run a couple miles every now and then and see what it's like firsthand.