You are told that you are getting a permanent “earworm” that would be in the back of your mind when you are awake until the day you die…but you get to pick the song. However, if you try for a work-around like John Cage’s silent work 4’33", I’ll pick the song for you. 
Remember: If you pick your favorite song, there’s a very good chance it will become your most hated song in a week or so.
“Live and Let Die.” A slow section, a fast section, a funky section, brass and strings, it’s got it all.
You got to give the other fellow HELLLLLLLLLLL!
Am I allowed the Abbey Road medley?
Probably not. I’ll go with **Uncle Albert **by Paul McCartney. Some variety to it.
mmm
I’d go with both the Beatles, and variety: Revolution #9.
Full length American Pie. At 8:33, I won’t have to hear it as often.
Well, I know what I wouldn’t pick.
Would that be a certain dessert that randy high-school boys…nm.
Elaborate, please?
*Rio *by Duran Duran?
I think I would pick Baker Street.
Fourth Movement of the Ninth Symphony by Beethoven (Ode to Joy), instrumental only, without the German shout-singing.
There are a number of album sides that are a single track: Yes “Close to the Edge”, Genesis “Suppers Ready”, Jethro Tull “Thick as a Brick”. All would make acceptable rest-of-your-life earworms. However, I think I will go with my current actual earworm, “La Villa Strangiato” by Rush.
Dammit. You preempted 4’33" and songs of its ilk designed to get around the spirit of the question.
I can probably survive Neu!'s Hallogallo as the background music to the rest of my life. (Note: this is an actual song I listen to with some frequency, not a throwaway answer, and it is earwormy to me.)
Shameless cheating: The Art of Fugue by Bach. Bonus: The big moment in it is famously unfinished, leaving me with a “what-if” to contemplate over and over.
I wouldn’t pick ‘Cherry Pie’ by Warrant.
If you try to pull something like that, you could get “Music Box Dancer”, “This Is The Song That Never Ends”, the "“Levan’s Polka” loop…or worse.
Rachmaninoff’s Third Piano Concerto: 3rd Movement.
edited
Sleepwalk by Santo and Johnny
Tubular Bells by Mike Oldfield. It’s long enough not to get too boring on repeated listens.
Obvious joke too obvious…
We have a poster here by the name of the piece I would choose: Mozart’s K364, the Sinfonia Concertante. 1st movement, if I must.