I would go for one of the Intuos models - I have the Intuos 3 in the 6 x 11 size which I love (my earlier intuos was the larger 12x9 and was really a bit big).

I had thought of upgrading to the 5 series because of the touch capabilities (not for Photoshop or Illustrator) as I often find myself doing that on my tablet and wondering why nothing's happening! I saw some negative reviews for it, so I shelved that idea for the moment. You might check that out before buying,

I figure they would all do the job and it would depend on your budget. I have a small cintiq and it works great. Before that an Intuos4 which was good. @Cthoman I used a mouse for years and I think a lot of Adobe Illustrator users do.

If you don't want to spend a lot of money, and just want to try it out for a time and get used to it, and only need the basics, you could start with the Bamboo or the other Bamboos which have various other enhancements like wifi and touch capabilities.

I just bought a small Intuos 5 because I want more capabilities, like the pen-tilt function in the pens that only comes with the Intuos models. I am working in PS and Painter, though, using the brushes. I have the small size (used a small Bamboo for a couple of years previously) and haven't found a need to go bigger. Unless I could afford a Cintiq!