It all depends which ports of call you are about to visit. As for me I usually mix planning what do in some ports of call and in others I can buy an excursion. E.g. if I`m into some kind of activity like snorkeling - I like to do it via excursion. If the port of call has a lot of historical places of interests or I wanna do nature sightseeing - I usually make planing with my husband beforehand and we know the route that we gonna go.

Btw, if you are travelling in a group, I suggest you to rent a little car(bus) - you usually can find lots of guy how promote their excursions directly in the port (you will see them when step out of the ship).Soinour case we were cruising in a group (5 person) and we came to that guy (actually he wanted to find a group of 10 people). But we said that there are only 5 of us and showed him the list of places that we wanted to visit. So we paid him $200-250 for the whole day and he was doing for us a personal excursion. It was great! We did it several times (on Grenada, Dominica, Santa Lucia). And on Saint Thomas we just took a cab for $4 per person to the beach. And on Curacao we just went by foot to do sightseeing. As for me excursions on the ship are a little bit overpriced and if you like to make plans and do some research by yourself - then you can try. Wish you luck! I`ll be happy to share some other my experience if I could know what ports of call you are going to visit :)