I'd have to say that Beren and Luthien is my favorite. Because of that i also like Aragron and Arwen becuz those two relationships are basically the same. One of my favorite parts in the Silmarillion is wen Luthien dances so beautifully in front of Morgoth that he falls asleep and that gives time to Beren to cut a Silmaril out of the Dark Lord's crown. Even tho being a deutscher i'd have to say that that part is a perfect example of Amerikaner ingenuity