its not an either/or situation. you can juice everyday and eat whole foods too.
juicing liberates nutrition and puts it in a very assimable form. some people's digestion is compromised (most people actually) and juicing on an empty stomach is the surest bet way of getting plant based vitamin and minerals.
i eat whole foods everyday, and i juice about 5 times a week. thats the formula that works for me. there is something special about fresh juice first thing in the morning that does not happen with any other food or supplement.