We use stable, Current Design or Eddyline tandem kayaks on all of our kayak trips. These are very big and carry a lot of gear, and can be used as a 3-person kayak if a participant needs to sit in the boat as a passenger. Everyone will get the opportunity to paddle and stern a boat if they want to.
On some trips we use Wenonah canoes made of either Royalex or Kevlar depending on the location, participant group, and portages.
On other trips, particularly on big open water like the Mississippi River, we use our custom, handmade 24-foot North canoes. These boats are specifically designed for safety and stability. Each boat fits 10 people.