Anything WACOM makes is the shit, even the cheapest ones. Never buy any other brand. I have an intuos3 A5 wide for around 400eruos and it delivers professional quality, there is no real need for anything better other then bragging rights. In fact, the only reason i've got a wide is because of the widescreen laptop, A5 is just fine. A6 is somewhat on the small side but perfect to start with. I started with a second hand WACOM A5 that was total shit and needed its own power adapter, but still, its better then a mouse.
The pressure sensitivity makes a huge difference because you can set either brush size or brush opacity to it, which doesnt only greatly speed up the paining process but makes it a hell of a lot easier and more intuitive.