This one might be tougher for some to figure out, and i put up some of the more well known songs from the series, so take your pick! And always there is other for those who's favorite song isn't listed(it's already long enough as it is!)
For me, my favorite song would have to be To The Outskirts Of Time. The song is very touching, and hearing such an awesome song also after beating Lavos, I don't think they could've done anything else to make the song feel so much more rewarding, and with the whole feeling of them getting to see everyone again as the song is playing also makes it just so much grander, seeing every single environment, and even without visuals you can put in your own just with the melody which grandly says more words than any artist could ever write down.
Poll