There used to be a "wizard" that helps you pick which tablet is best for you on the Wacom site, dunno whether or not it's still there. It depends on how you are accustomed to drawing. If you tend to draw/paint in large, sweeping arm movements, you'll want a large tablet, no matter the size of your drawing. If, on the other hand, you tend to draw/paint with small wrist movements, you'll want the 4x5 or 6x8.
I've been using a Wacom for several years, and the only reason I have a 4x5 Graphire (bought after my 4x5 ArtPadII, bought after my 4x5 ArtPad) is because I can't afford a 6x8 Intuos2. If you can, or if you can save up for it, go for it.
Oh... one other reason to go with 9x12 or 12x12 is if you do CAD stuff. From what I've heard and read, tho', the 6x8 is the most popular model among graphic and fine artists who can afford it.
Hope that helps.
I've been using a Wacom for several years, and the only reason I have a 4x5 Graphire (bought after my 4x5 ArtPadII, bought after my 4x5 ArtPad) is because I can't afford a 6x8 Intuos2. If you can, or if you can save up for it, go for it.
Oh... one other reason to go with 9x12 or 12x12 is if you do CAD stuff. From what I've heard and read, tho', the 6x8 is the most popular model among graphic and fine artists who can afford it.
Hope that helps.