Two very different choices. I don't know that much of The Proclaimers beyond their first two albums but they have always struck me as genuine guys who write heartfelt music. They're quite sentimental but the older I get the less I care about being seen likewise.
Though Sexy Boy was Air's big breakthrough big hit, I think it does them a bit of a disservice in terms of showcasing who they are and what they are about. There's better on Moon Safari which is quite eclectic as is much else of their work.
If it had been a different Air song it would probably have won but I'm going with The Proclaimers.