I originally voted for Leviathan, but for reasons stated by @Labbes, it’s probably not the worst. In fact, with Multithreaders, you could do a lot worse in criminal for breaking code gates frequently, in a deck with lots of drip economy.
Sayonara can break a lot of stuff, but not a lot of commonly played stuff, not as much as Leviathan, and not at the great values of efficient either. But it’s easily better at rush.
@ErikTwice, I’ve totally put Aurora in a deck. Oops. That being said, it’s still a better icebreaker than Wyrm, but not a better card altogether.
Alpha requires a lot of work to get working, and it was unfortunately costed. If you’re Kate and you mod it out early game and you are running Inside Job, congratulations, you’re playing with old cards.
NFR is nuts, it completely invalidates barriers, and it’s really not that hard get going with Datasucker support. Add in some The Turning Wheel so breaking barriers that you have no intention of getting much further past is still a good thing. It sucks to get it trashed, or bounced, but undoubtedly, so does Alpha.
Force of Nature is the worst breaker in the game, easily.
Creeper is not.
I love these polls, and I love judging cards thusly.