I don't know how you can pick just one. I have different favorites for different times and/or periods in my life. Big Deep Purple fan and love Speed King and especially highway star, when riding. But back in 8th grade, my sister, who is a very talented organ/piano musician, worked for months on a difficult arrangement of an old song called Deep Purple that I thought was incredible. In HS, the song Temptation Eyes by the Grass Roots was synonymous with my crush at the time and so on. I'm a percussionist and love "Frankenstein". I practiced weeks to get it down pat so our band could play it (back in the 80s), but no one wanted to since it had no vocals(or recognizable words at least). These days, every once in a while my wife gets on YouTube and plays late 60s & early 70s. We have several that have special meaning for both of us, but I like almost any songs that have horns. Love Maynard Ferguson stuff.