I participated in both the Shem Creek and the Isle of Palm 3 hour kayak tours. Both tours were the full 3 hours. Both are excellent.
Guides on both trips were excellent, very knowledgeable about the wildlife and eco-system. Answered all questions. Guides and staff at both locations were very accommodating of all participants, of varying skill, strengths, and mobility.
The Shem Creek tour traveled up the creek and then back down to their dock with a short trip extension towards the Charleston Bay. Some tour participants saw a dolphin, very briefly.
The Isle of Palm tour took a circular path through and around the salt water marshes, with a short stop on an island where the guide showed us around and explained additional facts about the marsh plant and wildlife.
I preferred the Isle of Palm tour mainly because of the circular route as opposed to the out and back route of the Shem Creek tour.