Not love-lost, but so sad it still chokes me up, tho I've been singing it for 35 years...The Great Silkie. Every time I sing it I hope it comes out differently, but it never does.

For most wistful song I nominate Close Your Eyes, by J.Taylor

For happiest...hmmmm...can't think of a definitive happy song at the moment...but for contentment...You Aint Going Nowhere, by Dylan. Singing that always makes me feel good.