Consider your desk space. I have an Intuos that's pretty big, so it's kind of a drag to use at times.
Bigger space, however, allows for more sweeping, shoulder movements (which is the preferred method for doing less detailed stuff, traditional animators will tell you to be gestural).
With bigger space comes bigger cash requirement to buy it, however.
And, naturally, how much use it'll see. Will you justify the $300 purchase for an intuos, the $2000 for a cintiq, or will you feel a lot more comfortable with the $50-$100 in the graphire/bamboo range?
The advantage of the intuos above the graphire and bamboo is the tilt function and the increased touch sensitivity, which is missing in those lines. But it's more expensive, obviously.
