I use "feat." because it seems the most proper, but I put it in the artist name, not the song name. For example, say the song is "Drunk in Love". I don't have it listed as "Drunk in Love (feat. Jay-Z)". I change the artist to "Beyoncé feat. Jay-Z". I do that with all of my songs with featured artists, so there's A LOT of artists on my iPod (as if there aren't already), but it helps for organizational purposes.
