Which is the best song for the acoustic duo?

My friend and I are an acoustic duo and we are looking for more songs to add to our setlist. We have a lot of favorites, and we are in the process of arranging them just right, but do you have any suggestions? We both play guitar, and I play the piano sometimes and I sing. I can also play the violin and my friend knows a little flute. Thanks! We'll do any kind of music.