When you're building a non-trivial JS application ...
I sense another round of discussion of this is about to begin, and 140 characters isn't quite enough to say what I want to say, so:
But do me a favor, OK? Don't base your arguments solely on the winner of a popularity contest. Don't tell me how easy it is to find developers familiar with one library or another, because I'll come right back and ask you just how good those developers will be at solving problems that aren't addressed by said library. And please tell me you've at least explored some of the other options besides [insert the library you're advocating here].
So, please: Tell me what solutions you've looked at for non-trivial application development. Tell me where they work, tell me where they fall short. Tell me what you're working on and how you chose the tools. Don't tell me why I'm wrong -- tell me why you're right. Deal? Discuss.