I have an 8 foot inflatable kayak, a sea kayak, and a SUP. The inflatable is a bit of a slug, but works as a dingy for my 19, and is good for exploring, especially small places. It is light and goes up on the cabin top easily. The sea kayak is 18 1/2 feet long and is a dream to paddle. It is fast, and you can cover long distances fast, and comfortably. It weighs only 36 pounds, but is a bit of a challenge to put on top of the C-Dory mostly because of it's length. It is very comfortable and provides a good work out for the upper body and legs. It is very stable and will go anywhere I want to go. It also is a nice winter craft as you can stay very dry and warm (with a spray skirt and proper clothing. It is a challenge to enter and exit from the C-Dory.
The SUP is a workout. It really makes you focus on your core muscles, and it is great for increasing balance control. For me, it wouldn't make the most perfect dingy, but in warm water areas it is great for exploring and exercise. I have tie downs so I can take waterproof bags and even a fly rod along if I want. It is much more maneuverable than the sea kayak in tight places.
I think if you are traveling in areas where the water temp is a swimming temp, and you wanted to poke around and explore, a SUP is a fun way to go. If you want to explore marinas only, I think a small kayak would be better suited for that. If you are on a SUP, straight line travel is much easier that tight turns. The faster you paddle, the higher the board "floats", and you have more control. When I am on my board I am prepared to swim at any time, and marinas are not the safest places to be in the water. A SUP can also be used for shore transportation, and you can ferry some items from the beach to the boat. I think the perfect place for a SUP is on Lake Powell.
This couple carried their SUP's on top of their 22 C-Dory and used them for exploring the small bays and canyons on the lake, and for their daily workouts.
Robbi