Small groups are usually defined as between 10 and 24 travelers, often less. If you're the kind of person who enjoys more intimate experiences and personal service this is a good choice. All else being equal you will pay a premium for this style vs a larger group tour.

Groups are between 25-60 people, typically ~30-40. Usually there will be many opportunities to split off and enjoy meals and excursions in smaller groups. This is the most economical way to travel, saving up to 40% versus booking the same itinerary yourself.

Private tours give you the undivided attention of a guide, and often involve special access to sites and unique experiences not available to larger groups. This is a great option for families, couples, and small friend groups. Expect to pay a bit more for the extra service.

A travel company plans your itinerary and arranges all the logistics including lodging, local activities, and transportantion. You have the flexibility of a solo trip while still getting the convience and time savings of expert planning. Get 90% of the benefits of a tour, without a guide.

These vessels are smaller than most ocean cruisers, limiting which amenties are available. Passenger counts can vary. One of the biggest advantages of a river cruise is the ability to dock at smaller ports and local villages.

Similar to a self guided tour, this usually involves a home base, such as a hotel or resort, with packaged activities and day tours as a part of the stay.

Small ship cruises usually have a max passenger count of 500. The primary purpose of these trips is to spend time off the vessel in local ports (e.g. Mediterranean) or experiencing nature (e.g Galapagos or Antarctica). Cabins can vary from budget to luxury.

This is the "floating city" experience, with multiple ways to enjoy your vacation aboard the ship as much as on land. Ships are multiple floors, provide several activities, culinary, and shopping options. They often make fewer stops and have less time available for shore excursions.