Just got back and i would say do sting ray city, it was a blast. we booked through Soto's Snorkel Cruise so we didn't feel like we were part of a herd and they were only $24 dollars a person with pick up to and from town. it was great! and they also stop at two other stops to snorkel.
did dunns river falls too and would recommend it but as most have said shopping in town got ugly. too aggresive. even as you leave the falls they are very aggresive but at least those little shops are more supervised. don't go to the flea market in town. My daughter did get her hair braided there for a decent price, but they got me on my other daughter. they told me $50 for the one daughters whole head which i thought was reasonable but then my other daughter just wanted the front so they said $2 a braid. Silly me, i never thought they would fit 20 braids in the front of her head. So don't go for that one. Get an exact total price for what you want done up front.
If i were to go back there i would most likely do the river tubing tour through the ship or one of the tour groups. oh and we didn't book dunns river through the ship, we took a cab there and paid the entrance fee. the cabs are right there at the dock.
whatever you do, have a great time! we loved it!