Bach and Mozart. Yeah, they were pretty and tinkly and not exactly avant-garde, and a lot of their songs go on for like half an our... but that's what I like.
That said, I sort of get the sense that it's not only about the music anymore. A lot of other stuff gets added. Maybe it was different at the time when these classical musicians were still alive, maybe they had scandalous personalities which meant that people wanted to hear their compositions and not that people genuinely thought the compositions were any good...
But I also can more easily appreciate music that comes with a context. Words. Orchestration. Maybe it scored a really touching and memorable part of a movie or television show. With a lot of ballet composers, maybe it comes with the dance. Obviously for opera and Broadway musicals, it comes with a story. And then there's the story behind each song, of course-- I would like Taylor Swift's peppy songs even if I didn't know who they were about, but even though I don't generally read gossip, the "muse abuse" gets in there. Adele and Jason Robert Brown cannibalized their "muses" too, but don't get as much flack as Taylor Swift for it.
Basically I wonder if the real test of time when it comes to a song is how good a song it is, when people aren't caught up by whatever else might have been added to it to make it popular.