I use a 6x8 Intuos2, myself. I like the higher level of pressure sensitivity, especially when touching-up photos or drawing in Illustrator. I think the pen it comes with is more comfortable and the cordless mouse it comes with is nice too.
It is more expensive, though. But they last for freaking ever.
One word of advice...if you have more than one user on your Mac and use fast-user-switching (I'm assuming you're using OSX 10.3+) make sure you go to Wacom's support area and download the latest driver for the Intuos. It's the only one that works with fast-user-switching.
Have fun!
JimC