This question is hilarious because the answer is painfully obvious.
The Catalyst was Linkin Park with a whole new suit of armor. It confirmed right out of the blocks that A Thousand Suns was going to be something really special. It was fearless, energetic, different and went against the grain. It explored different moods, sounds and dared to do things we rarely hear come from this band.
Burn It Down, while a fun song and I do enjoy it, is an old hat trick, but with a different hat. It's not as energetic, it's not as exciting and it makes me worry about Living Things. When I listen to it sometimes my mind flounders and I lose interest in the song. But whenever I hear The Catalyst it has my full attention all the way through.
I might go as far as to say The Catalyst is Linkin Park's greatest song-- How dare I? Even if it isn't, it's damn close and Burn It Down doesn't even scratch the paint that The Catalyst covers.