abelmanmoth, is that Eno one the one that's often used in adverts and TV shows? That sounds like it's entirely made up of ghostly chord changes? It makes me tingly, if it's the one I'm thinking of.
One song - that's tough. It'd be a toss-up between: Beatles, Penny Lane. I've always leant more towards the Macca songs and this one sums up the art of catchy pop-song writing - perfect length, perfect tune, every little change up or down is spot-on - it pushes all the right buttons.
Or - Radiohead, Planet Telex. It's got everything I want in a rock song - great textures, every kind of guitar sound, wonderful dynamics, an economical but odd/baffling lyric, oh man it's just wonderful.
Neenee you sneakily haven't stated yours, despite asking the question.