To make it short: Harmony is smoother and more aromatic and has more yellow tips. Melody is a little stronger, has more body and substance. Both go very well with milk, Melody is just a hair better.
I am finishing samples of both right now, drank the last of Melody yesterday and have one more tsp of Harmony in the tin. Still I am undecided which of them to reorder - both are beautiful teas. I may just have to get both.