It depends on many variables. Your dedication to art/animation, your desk area, and your price limit.
I started out with the bamboo tablet. It worked well, but there is definitely cons.
Pros: Cheap(70-100$), Compact, Lightweight, got the job done.
Cons: Has alot of detection problems with Vista, Pressure sensitivity isnt too acurate.
If you are just trying to make low quality flash movies for newgrounds and dont have enough money, I would go with the bamboo.
Now, the Intuous4 is a bit more expensive, but you do get what you pay for.
Pros: GREAT pressure sensitivity, precision mode is boss for animation, good size(depending on what size you get), and the side buttons are overall good.
Cons: A bit pricey(260ish), does not have a draw-on interface like the cintiq.
This is a good tablet if you want to make higher-grade animations.
The Cintiq is considered the industry standard.
Pros: Considered best Wacom tablet, Pressure sensitivity is unreal, draw-on interface
cons: ALOT of money!