What a great quilt. So cheery. My first inclination is that great light blue solid in the quilt would be a wonderful first border. My second choice would be yellow. Very narrow to "stop" the quilt. Then your white border or a white on white, like polka dots, and also a white binding. That would be a very clean and vintage look for this cheerful work.
Go wild on the backing and find a fabric that has all the colors in the quilt top! WOW!
peace :D