This depend of your screen size, If you have small laptop screen, let say 15" or smaller you can try a small tablet, but with a larger screen you should prefer larger tablet. To make your drawing feel natural you have to make the movement of your hand the most similar to the result on the screen. This is why it's much easier to draw on a cintiq, your movement is exactly your drawing.
i went from a genius tablet nothing special to the intuos4 small and i love it learned everything fast mapping , setting etc... if i needed anything to learn i asked my friends or just youtube it .. either way you will always get better. keep the art going hope you find the one for you
Probably better to start with the larger Bamboo and then, if you really use it a lot over the next year or two you can easily justify spending the money on a proper intuos 5. The small tablets aren't that great for drawing because you can't really get the long strokes that make a tablet useful in the first place. The pressure sensitivity isn't really that much of an issue if you're just starting out. The Bamboo has more than enough.
There are also build-quality things that make the intuos more expensive but if you take good care of the things it won't be an issue.