It all depends on how serious about it you are. Bamboo if great for basic use, for majority of amateur artists it will be just enough.
Intuos is step above it, both price and functionality, it's semi-pro up to pro, if you can afford it and actually will use it regularly and maybe even make some money off your work that's what you should aim for.
Cintiq is if you are full blown professional, especially the 21UX. Those are the series with display screen that allow you to actully draw without looking at your PC screen.