Although highly subjective I would appreciate some input.

I will be in Utah in early May 2015 and have 12 days to apportion between Arches, Canyonlands (Island and Needles) and Capitol Reef.

Never having been to any of these parks they all seem fantastic as are their descriptions in "Photographing the Southwest".

I plan to do day hikes but no backpacking, and will have a 4x4. So far, I plan three days in each.

Is there one that is worth more time than the others, given my time constraint?

If I can squeeze in a couple more days which of these parks deserves the extra time?

Any advice from those who have visited would be appreciated.