Going to Road to Hana is a beautiful experience, as you'll get to see many high cliffs that hug the north shore coastline with numerous waterfalls, gulches, and streams that line the landscape. Why do it on your own?
Valley Isle Excursions takes the stress out of the journey by transporting you towards Hana and back around the southern loop on this one day 10-11 hour bus trip touring East Maui.
I personally had a great experience, and that experience was compounded by the ever awesome tour driver I had, whom was Pu. If you have Pu as your driver, be prepared to be deluged with great local Hawaiian and Maui knowledge.
Overall, Valley Isle Excursions takes care of you from the moment you step onto the bus, to when you get off. Check out my more detailed review of them here: http://www.hustletoparadise.com/2012/12/01/road-to-hana-with-valley-isle-excursions-review/