I like the one with the green background mainly because of the composition of the flowers, if you notice the 2 main flowers are facing the viewer where as in the blue pic only one flower is facing you, the second one is lower and facing more to the right and you lose that open look of the blossoms in the first pic. ALIAS
I prefer the blue background as it complements the orchids and find teh composition of that shot more engaging
I really like the blue. It complements the purple and the stem fades in with the black shadow on the right. Very cool.