My own suggestion would be the intuos.
http://www.wacom.com/en/Products/Intuos.aspxIts mainly designed for drawing with the pressure sensitivity and all its features. But its accuracy and custom keys make it great for after effects. Like mapping the 2 pen buttons to forward and backward 1 frame.
The pressure sensitivity also works with the rotobrush the lighter you press the smaller the circle allowing for quick adjustments to the size and accuracy of the rotobrush.
Its down fall is its size, I have a medium so I cannot have it on my desk the entire time, so I don't use it for quick masking of 30 frames. But if I know I am going to be sitting there for 3 hours rotoscoping I get it out. Price wise its a bit dear but its not hugely expensive. Mine was $500 AU. Intuos4 not intuos5