This was a really hard question. I couldn't decide between The Master Sword and a crowbar. They're both amazing, but exact opposites. The Master Sword is greatness incarnate. Glory, power, justice, good conquering evil. All of that good stuff.
The crowbar, however, is like showing us how something so ordinary can do amazing things. It doesn't have to be flashy or immediately recognizable as something to count on.
In the end, I chose the crowbar, because I'm a sucker for "everything is not what it seems". However, I love The Master Sword too.