What rapids (normally classified by class/grade) do you want to paddle? The only boats that would fit your current criteria would be the Pyranha Ammo and Bliss-Stick SCUD, but i'm confused on what you're looking for. Look at this link to get a better idea of what you want:
adrian.playak.com/index.php/articles-mai...rted-choosing-a-boat
Once you have decided what type of boat you want, it will be much easier to narrow it down, and then you should try to find a few models that fit in that category, and at this point, just get the boat that is the most comfortable (you probably won't notice the characteristics as much earlier on). Most current boats have adjustable outfitting, and it is really helpful, especially on the hip pads (the owner/salesman should know what adjustable outfitting is, and you should have them help you outfit the boat before you buy it). You are going to be better off finding a good used boat, because you will probably have a better idea of what you are looking for after a year or so. A few things to watch out for are cracks, dents, thin plastic (it should not flex too easily if you push into it hard), deep scratches (especially on the inside, because it will create a weak point) and oil canning (it looks like someone hit the bottom of the boat with a hammer, and is normally very easy to spot).