I am shopping for a first kayak. I have only been kayaking a few times on rented boats. I am a heavy paddler at 235 lbs and 5'6". I will be paddling primarily on a slow river (and sometimes lakes).
I am looking for two recommendations:
1. What size kayak is appropriate for my situation? What is the largest that is reasonable for rec/fitness use on a slow river/lake?
2. Any particular models I should be looking at or avoiding?
If you're looking for a large-cockpit "recreational" kayak, there are many options. Some of the lightest are made by Hurricane Aqua Sports, and Eddyline has a couple of light rec boats as well. But in the kayaking world, you will generally have to pay more to get less weight.
Some of the more popular rec kayaks are the Wilderness Systems Pungo and Pamlico series, the Old Town Loon and Dirigo series, and several of the models from Perception.
I'd suggest staying away from anything shorter than 12' -- shorter boats tend to be frustratingly slow if you want to go any distance or against the current.
If you'd like a bit more efficiency, and are comfortable with a slightly narrower boat, you might like something like a Current Designs Kestrel, Necky Manitou, Perception Carolina, or one of the longer Hurricanes.
Sit-on-tops are a good option for some folks, especially those who swim/dive/fish from their kayaks or who are worried about self-rescue.
Test-sitting will narrow the field, and test-paddling will tell you more. The "best" kayak is going to be different for everybody. Only you can decide what works best for you.
Riot Voyager I am about the same weight and height as you and also paddle in slow moving water. I got a Riot Voyager from the classified ads on p-net. I had previously rented and borrowed boats and settled on this one. It has a comfy cockpit which you can brace your thighs to rock and cut with, but it is still open enough to ease entry and exit. I was surprised at the combination of maneuverability and tracking, although the tracking does require good paddling technique (as mine improves, so does the tracking). It also has great secondary stability, but the initial stability is low. This makes it great to cut, but surprisingly hard to dump. Good luck, and welcome!