In my minds eye, I always like smaller, to emphasize the detail work of something along this idea.
That being said, there's a whole lot of curved seams to do for this quilt and curved seams are not always the most fun!
Maybe do some sample blocks and see which size you like working with better. In this case, larger blocks/circles will be easier to get the curve right. Then use those sample blocks for some mug rugs and the like.