If you want to go to Dunns River Falls avoid the Carnival excursion. Peat Taylor will take you up there much quicker and you will be amongst the first to climb the falls (which is a wonderfull experience). When youre done and return to the visitors center you will meet the long line of Carnival guests waiting in long lines!
After the falls he gives you a nice tour of Ocho Rios and the the area around it, tells you nice stories and even sings an occasional song.
Its a great tour and a nice guide for a decent price. They drive you in small mini buses which gives it a more personal touch than the big tour buses.
Also he was actually the one who mailed us and told us that Carnival had reversed the itinerary due to the storms and confirmed that he had changed the dates for the tour accordingly. We were never informed by Carnival about this...!?!
http://ochoriosjamaicatours.com/