I used to think How To Disappear Completely was it. When I died, I would want that played. It's an absolutely magnificent song, and of course the 'I'm not here, this isn't happening' lyrics combined with wailing would be fitting. I still absolutely adore the song, perhaps slightly less now that I've delved deep into Kid A and the whole album clicked in that 'good glorious fuck, this is beyond description' manner.
But Motion Picture Soundtrack may just have the upper hand. First of all, the backing evokes stars twinkling in the night sky; secondly, the organ hits you so hard in the chest cavity it bowls you over; thirdly, the line 'I will see you in the next life' is just unmanageably beautiful. But that's not all, oh no. The bit where it comes back in actually sounds like someone ascending to heaven. It throws a lot of weight behind the notion of Kid A being a cradle-to-grave concept album.
God, this makes me a bit of a sadistic bastard wanting my funeral to be an epic tearjerker. Only if I die young, maybe.