Not to be contrarian, but I've got to shout out to smoothies. I do better with smoothies than juice--with the fiber removed, juice is reduced to sugar (and nutrients) and water, which can be a lot for one's system (at least mine) to take. Whole fruits, fiber included, digest more slowly than just the juice. For some reason, the whole thing blended sits better with me. I guess the actual answer is the most annoying possible one: "it's different for everyone, so try it out!" (Grumble.)
Make sure and peel things before you blend 'em. I've also had great luck with putting spinach in any smoothies. If you get really into it, you may even want to invest in one of those mega-expensive, high-powered blenders, which reduces everything to a juicelike pulp. Best of both worlds? I'll let you know when I have $500 lying around.