I use a little biddy five by six wacom tablet, and it works amazing. Anything bigger would probably work better. But, from my point of reference, Wacom is the way to go.
I have a Wacom Intuos 2. 9x12 I believe. Works great, but as it gets on in years, the pen tends to act a little funny. A replacement pen may be a good investment.
I use it for pretty much all of my art, so it has my seal of approval, I guess.