I quite liked the idea of Ginny and Luna together. Ginny is already shown to be pretty close to her, more so than any other character and they'd be a nice clash of personalities. I like the image of Luna cheering Ginny on at a Quidditch match in whatever quirky way she pleases and an amused Ginny shaking her head, but secretly loving every moment of it. But the moment anyone dares make fun of Luna for it, Ginny would be sure to let them know how she feels.

Harry/Luna has a lot of good merits, but I can't imagine Harry would ever laugh with her quirks instead of at them. His complete lack of interest in her other world curiosity would be a big issue, hence why i think they work better as friends. I think given the options, Harry/Hermione make the most sense.