Typically I'm in favor of dark and lots of pattern and not a huge pastel person, but in this case I think the lavender is WAY better.
-- The lavender really goes well with the creams and is a nice transitory note between them and the darker purples in the quilt. It lets you white point and your black point be within the pieced pattern and puts the focus where it should be.
-- The flower shape in the dark fabric draws the eye away from the piecing. It is more circular than your diamond design. Typically the similar round shapes would work well together, but eyes are more drawn to circles than rectangles so instead of being a subtle shape repeat the flowers are an equal draw for attention, even though your mind knows the big pieced diamond should be the star. This makes the border look eye catching, but also makes me miss the subtle details in the pieced fabrics.