This is a tough one because it all depends on what look you want to achieve.
the rose sets the blocks off beautifully,, decorative stitches on the edge will work
the green works if you are looking for a softer feel.
The blue doesn' t work for me at all, does nothing for the blocks,
the purple would work if you are looking for high contrast
It' s. All a matter of taste & the feel you are tryinng to achieve.