Baloonatic

Beautiful job! Whatever you decide, preview it and take a pic so you can compare the different looks on your puter. My taste would lean toward a first border 1" wide (finished) of one of your dark colors, green or blue. I think I'd try and keep the second border simple as you have a lot of movement going on in the quilt. Perhaps use the quilt's scraps and make flying geese flying horizontally, or continuous half square triangle strips. Then bind with the same fabric as the first border. Alternately, keep the first border very simple and then bind with scraps of the leftover fabrics.
Here are 3 pics that may give you an idea