Currently i have a Teclast which is the Telechips version but plays xvid (which in a way quite similar to Rockchip), Sunplus (.AVI & .3gp) and Actions (.AMV).
Both the Teclast videos and Sunplus videos are quite the same. Sunplus supports upto 30FPS, so videos appear to be quite smooth.
Definitely video-wise, .AMV format could not be compared to .AVI format.
I'll probably rank Rockchip & Sunplus side by side in terms of video quality. However, Rockchip would still have a slight advantage as the xvid codec allows much smaller sized video files as compared to the pure .avi for Sunplus. i encoded a 3minute+ video at 30FPS (2.4" size), resulted in a filesize of 30MB!