For flatwater, you might consider a solo canoe. They can be just as manuverable as kayaks – it’s all a matter of the boat’s shape and beam. Some kayaks wallow like pigs and some shoot through the water; the same is true of canoes.
This is from Placid Boatworks:
“Solo canoes designed for use with double-blade paddles were popular during the first blossom of recreational canoeing at the turn of the century. The double-blade paddler almost doubles the single-blade user’s stroke-per-minute rate and increases speed. Double-blades allow smaller paddlers to keep up with, and even outrun, skilled single-blade users. Beginning paddlers can easily drive a canoe or kayak in a straight line with a double-blade paddle.
The difference between double-blade canoes and kayaks is deck and weight. The choice between the two should be made according to the water paddled. Fresh water, especially here in the Adirondacks and in places like the Boundary Waters, often requires portages and open topped canoes are lighter than decked boats. They are also easier to load with gear, and easier to enter. High sides keep waves out, and on fresh water, a windward shore can usually be found for protection from storms.
Kayaks are designed for open water where portaging is not a factor. As hull weight is unimportant, kayaks are decked to stay dry. They require spray skirts, complex entry and egress procedures and special skills, such as the ability to perform an Eskimo roll.”
You should also take a look at sit-on-top kayaks, since they combine many of the best features of canoes and kayaks and are great for lake and slow river paddling. But if your rivers are fast and curvy, you’ll need to lean into turns and will want higher sides than sit-on-tops offer.
You don’t have to do it by renting, but absolutely try before you buy. The best and cheapest way to do that is to attend a boat day, where a local shop brings a bunch of their boats out to a lake for people to try. Boat days are usually in the spring, and there is zero pressure to buy – many people will come out just for fun, or to try paddleboarding for a lark. And many shops will be happy to take you and the boats you’re looking at to the nearest water for a spin, any day of the year – though there is some pressure to buy in this situation.
Disclaimer: I am a flatwater kayaker who wishes she bought a canoe instead. I love calm rivers best, which always require a portage or two – and portaging is such a bitch, even with my little 25 lb ‘yak.