I suggest Keep #1 and Kill #4. . . .
I really like them all and would suggest keeping all, but out of them all, #1 is the one to keep with its amazing shades of pink, purple and blue.
Since you asked to select one to Kill, it would be #4, because of the limited contrast in this photo.
Oddly, I'm not really sure of #5, the dark shades are not attractive, but then again, they are intriguing. This is probably the one that sells for the highest price.