I have heard the phrase attributed to Shakespeare, "Of all the flowers/the rose is the best/" but I don't know where it comes from.
The line you are thinking of is actually "Of all Flowers, me thinks a Rose is best," and is spoken by the character Emilia in the play "The Two Noble Kinsmen." This play was a collaboration between Shakespeare and John Fletcher. (This attribution was disputed for some time, but is now generally accepted.) It was probably the last play Shakespeare worked on.