There's a ton of different types. Check out www.texaskayakfisherman.com for some deals on used ones as well as a plethora of kayak info. Size and types depend heavily upon you and your build/weight and it's use.
I fish the bays from sit-in kayaks. They're great for protecting your legs from the sun. They're also easy to outfit using simple hand tools (saves a ton o' money). Generally speaking, sit-ins are faster than sit-ons, but they don't get up on plane too easily, either. Other than that, they take second chair to sit-ons.
If a sit-on is capsized, it floats. Not so with sit-ins. A lot of time, money and thought have to go into adequate flotation for a sin-in. Do not trust the manufacturer's flotation.
Mounting up in a sit-in is no easy task, but after you're seated, one's about as comfortable as the other, and after a bit of familiarization, stability is not an issue. ( I work about 70 feet of line with my fly rod out of my sit-in without a problem.)
Try as many kayaks as you can before you buy. The results may surprise you. For the price I was willing to pay for the kayak I was cionvinced I had to have, I bought three Pelicans. For me, they tracked better than the expensive model. For you? Maybe not. Try a smany different models as you can.
A previous post noted that yellow attracted sharks. It attracts reds, too. And who among us wouldn't be willing to loose a leg for the chance at a 30" red on a #7 rod?