What kind of fishing do you do? (do you have to stand up to fish?) moving water? Big bodies of water or smaller lakes? How far are you favorite fishing holes from the boat launch? (2-3 miles from the launch is easily accessible by paddling) with a kayak you do not need a launch, just need to be within walking distance.
The best piece of advice I can give you is find a store that will allow you to put the kayak in the water and test it out. Find a company that does demo days or will schedule a private session. Next I would read some reviews on what people had to say about their kayaks. The number and style of kayaks has exploded over the past 5-7 years and it is now about finding what kayak suits you best...its hard to say there is a perfect kayak that is super light, super stable and paddles like a breeze.
If you would like to be able to stand then something a bit heavier and wider would be your likely option. If you think you have good balance then you can lean towards something that is lighter, paddles easier and still be able to get away with standing up.
How much storage space do you want vs how much you NEED is another question to think about.
Lastly is the $$$ factor, I sold my boat knowing I was investing I in a kayak (they don't just go bad, I have a a wilderness systems ride 135 that is 6 years old but it is still in great shape and I prefer to take it fishing in the shallow marshes own here in Louisiana) They can get expensive when you start talking about the peddle drive kayaks but it is all about what you want and how you fish.
If you find a place that will demo a kayak for you, ask how much that demo model is....I got my wilderness ride as a demo model for $750 6 years ago and it only had small scratches on the bottom from them loading and unloading off the trailer.