If someone asked me to name my favorite song, I'd be hard-pressed. My answer to such a question depends on my mood, the time of day, the season, the weather, whatever. Still, if someone pinned me down and forced me to proclaim one song as my favorite Clash song, it would be Lost in the Supermarket. At least, that's the answer I'd give today.
The Observer asked a few well-known people what their favorite Clash song is. Two votes for White Riot, which might have been my answer at a different time of day/season/etc.