In many cases this depends on the situation and on where you are travelling.

Some places have only 4 or 5 tents or rooms, so a group of more than 8 people may need to stay in different larger establishments.
If you are organising a large family trip, the benefits of being together and experiencing the journey as a group outweighs being in small places or otherwise restricting your trip. In this case we will design your journey specially, and select suitable accommodation.

If you are a group of friends or can tailor your group size to the journey, the ideal size may be determined either by the groups interests (for instance hikers on a hiking trip in the Pyrenees should be content to hike the same distance and levels), or by logistical factors such as the amount of available seats in a safari vehicle (usually 4 or 6) or a light aircraft (a Cessna Caravan seats 10 passengers). If your group fills the transport units the cost per person is likely to be less.
We design journeys for many varied groups, but generally groups sizes of 6-12 people are ideal.