I'm a nervous traveler as well. I'd rather pay a few extra dollars and have the piece of mind that the ship will wait for me in case something goes wrong.
We did a mediterranean cruise for our hm and did all the excursions through Royal Carribean. I think it was worth the money to not have to do research about a million other options, have everything organized for me and have the ship wait for me. It was worry free.
I went on a cruide through Holland America and didn't do any of the excursions through the cruise line. It was really expensive and while I understood that the peace of mind of a ship-booked excursion would be best...my wallet ultimately ruled. We had no problems.
It depends on where you are going. I've been on more cruises than I can count and I've done excursions both ways. There are some locations where it is highly recommended that you stay within a certain area of the port and only book excursions through the cruise line, while other locations you'll be safe to book with independant tour guides. Do your research.
I typically always book on my own UNLESS it's an excursion that is supposed to take most of the port time (5+ hours). If it's only to a beach or tour, I can find my own way there for a lot less money.
I always book my excursions through the cruise line. it is well worth to pay the extra for peace of mind. On our last cruise, there were three passengers on our ship who took off on thier own and did not come back. The ship left without them.
Re: Cruise excursions
it will cost you a whole lot more to get yourself to the next island/port than the other company vs.ship excursion.
which ports?