We've been to GC 3 times on cruises and twice to Ocho Rios. All Carnival cruises.
GC: if you like beaches and just want to veg, 7 mile beach is heavenly. The first time we bought the excursion thru the ship and waaay overpaid. There are plenty of cabbies at the dock ready to take you to a nice beach. We liked the area behind the Marriott. No big waves and the water is beautiful. We've done Stingray City twice and it really is so neat. We always book that thru the ship just in case there's a problem with the excursion boat, the ship will wait for you. (Typically, if you book an excursion thru the ship and you're delayed, the ship will wait for you. If you go off on your own, the will leave without you!)
We're not big shoppers but there were typical island shops for jewelry and handmade trinkets. They're not very pushy in GC.
Now OR is another story!!! First time we climbed the falls and then went to a beach (ship's excursion.) Climbing the falls was really fun but my ds5 needed some help. (I guess ds9 and I did too at times!) Then we went to the beach which was nice, but not as nice as 7 mile. This crazy drunk with a bottle of rum was crowing like a rooster out loud many times. He would walk among the beach chairs and give plastic roses to women in exchange for "tips." We really just would give anything to make him get away. It was soooo annoying. Also as we left to go back to the ship, my dh was offered "someting special for YOU, mon" (meaning drugs) several times. Ugh! and relentless too!!
For our 2nd visit to OR, we didn't pick it as a destination. Due to Hurricane Wilma, we couldn't go to Cozumel as planned, so we were told months ahead we'd to go to Costa Maya. Apparently they couldn't handle so many ships so as we checked in we were told Jamaica would replace our stop in Costa Maya. We stayed on the ship and enjoyed the big slide on a near empty ship!
BTW, I still have a couple of soda coupons and arcade tokens for Carnival if you're interested. pm me if you want them.