We have done both. I don’t want to be accused of being silly or anything but there have been two times we would have been left if we hadn’t been on a Carnival excursion. The first time was because our bus had engine problems and the second time was because the tour operator had apparently misjudged how long it was going to take to get everyone down the Flying Dutchman zip line in St Maarten. He finally gathered everyone who was on a Carnival excursion and put us at the front of the line. Unfortunately, some of the people from our sailing were there on a private excursion at the same time and didn’t make it back in time.
Those are rare occurrences but I always try to do a lot of research when booking outside activities. I’m not a new cruiser nor am I a worry wart.... just aware of the possibilities and taking those into account when making a decision.