It's beautiful - I love your colors!
I've quilted a few bargellos for customers - I usually try to divide the quilt up into different sections, then put various fills in each, or sometimes diagonal lines to highlight certain sections.
Here's a photo of one bargello I did. You can see another example on my blog, scroll down to the end of the post - if you click the photo it will open a larger version.
http://andicrafts.wordpress.com/2010...own-two-to-go/