I've got a Trust A4, and tho it does require a lot of arm movement if used at full size, the degree of control is better.
The active area can be made smaller, so needing less movement, but if you have an A6, it is not easy to make it bigger!
Seriously, I think the A6 will be fine. I got the A4 because it is not a lot physically bigger than the A6 and was only about £20 dearer. Wacom are the best, but I think Trust are VFM.