What a difficult question! So many amazing genres of music and catchy melodies to consider! But if you could only pick one, what would it be and why?
1) I'm a big fan of Jason Mraz and absolutely love the lyrics, reggae feel and overall meaning it has held in my life over the years. (I also admire Jason for all of the contributions he has made through his foundation over the years).
2) I love the simple chords he uses in "I'm Yours" - this particular chord progression (1 5 6 4) can be used for thousands of songs - so by picking ONE song, I really have the potential to play so many others with the basic framework. (By the way, this concept is discussed more over at 8020Guitar.com)
3) It's a song that can be easily shared with others. If I can pick only ONE song, I'd love to go almost anywhere in the world and have the ability to connect with others through "I'm Yours".
What about you? If you could only pick ONE song to play on the guitar, what would it be and why?