The first thing I look at is whether there is anything unique about the tour. In October I am taking a Seabourn tour in Kusadasi which has two parts. The first part is a tour of Ephesus while the second part is a tour of a small village with a cooking class. If it was just the first part I would say, "Don't bother. Take a taxi to Ephesus and pick up a private guide at the entrance. You will have less people, more information and you can do it at your pace." Walking tours of Halifax, a visit to the New England Aquarium, the beach in Mykonos or lunch in Marseille you can do on your own in more comfort and at your own pace. But a cooking class for a limited number of people in a small town in Turkey. Even if you could privately arrange it, the time, logistics and hassle alone...no less even knowing where to start with such an event....makes the ship's tour an almost ideal solution. Others: a visit to a specific private chateau in Bordeaux; an early morning boat ride up close to glaciers; tours tied into onboard educational courses, etc.
The second thing I look at are the logistics of getting there, doing it and getting back to the ship. In August I am going on a Royal Caribbean cruise (Mariner of the Seas) and will be stopping in Cozumel. We will be taking the ship's tour of the Mayan ruins at Tulum. In order to take this tour you must take a ferry (more like a rocky boat) to the mainland, then a bus to Tulum and eventually the ferry back to the ship. While I could arrange a private tour and I do not relish sharing this experience with potentially hundreds of my fellow passengers, I relish less the thought of missing the ferry or it being delayed and the ship sailing without me. This particular tour is cancelled from time to time because of rough seas and the ferry is delayed at times for the same reason. When you are on a ship's tour you are protected from the possibility of the ship leaving without you. Doing it on your own is doing it at your own risk. I recall quite a few passengers left in Civitavecchia when there was a snap strike on the trains from Rome. The ship left them behind, without their passports, and the next port was in France. Independence is a wonderful thing...but I caution it should be exercised with caution.
The third thing I look at is whether there is a private tour option. There are many times when there is a private tour that is better than the ship's tour and it is (especially when paying for 2 or more people) less expensive. An example is a tour of Athens. In October I am providing those on my Seabourn Spirit Food & Wine Cruise a complimentary tour of Athens and Cape Sounion. Our guide will meet us at 7:30 am so that we beat the crowds and the afternoon heat. After providing us with a beautiful overview and explanation of the Acropolis from a nearby park we will arrive just as the Acropolis opens...before the crowds are even getting on their buses...and will be able to enjoy the site for quite a while ourselves. Then passing the masses as they arrive, we will head off to some of the other sites followed by a wonderful visit to the Temple of Poseidon followed by a waterside lunch in a nice taverna with a real menu. Doesn't that sound much better than climbing in a bus, standing on your toes to get a glimpse, shouting "Can you speak up. I can't hear you." and then waiting while "that person" just needs to make one more purchase?
The fourth thing I look at is price and value. There is a difference between the two. Sometimes you know you are being overcharged, but if you want the experience enough it remains of value. As I mentioned, sometimes a private tour is a far better value than a ship's tour, but then there are tours that you can only obtain through the ship. One example above is the cooking class in Turkey. Another might be a zipline in the Caribbean. Is that one hour tour - and 10 minutes of excitement - worth $80.00? For me there is no way I would spend that kind of money, but others would find the experience something to think back on and talk about for years.
We were in Tahiti last year on the Regent Seven Seas Paul Gauguin and took the Swim with the Stingrays tour as part of Regent/Jean Michel Cousteau's incredible and unique Ambassadors of the Environment program. Well, we thought this might be a bit better than Captain Marvin's private tour in Grand Cayman and was it ever. It turned into my family's first experience swimming with sharks (black-tipped reef sharks) and the beginning of their appreciation of sharks and a willingness to venture a bit out of their comfort zones to experience nature. Incredible value.
I also look to see if an independent option is available. Taking a walk to the fish market in Marseille followed by a wonderful bouillabaisse lunch does not need a ship's or private tour nor does a walk around Charleston, South Carolina with a buggy ride and some good ol' southern cooking. Halifax is a great place to wander and they even offer recorded walking tour rentals on the pier for only a few dollars. Le Lavendou, France has a wonderful local market where you can get lost for a couple of hours followed by a lunch seaside. Barcelona is one of the great walking cities where shops, markets food, culture, architecture, etc. come at you from all sides, but in a fun and not overwhelming way.
Theory is one thing, but reality is another.To be sure, independence is good for some and not so good for others. For many travelers the concept of not having to worry or having it all planned out is one of the very reasons they go on cruises. For that sort of traveler I would caution against striking out on your own. You can most certainly enjoy these cities and have the comfort of a tour, ship or private.
So when asking, "Should I take a ship's tour?" you should first ask what it is that you want to do, where you want to do it and might I be better off doing a private or independent tour. Only then will you be able to truly access the benefits and/or pitfalls of a ship's tour.