While it may be a bit belated to add my thoughts, I feel compelled to share my perspective on the various frameworks I have explored:
Among them are Angular, Knockout, Backbone, and YUI. After reading up on Ember as well.
In my experience, both Angular and Knockout take a similar initial approach by focusing on front-end integration. Personally, I find this aspect less appealing as it leaves ample room for error in designing a robust architecture. The burden of creating an effective MVC application falls solely on the developer with these tools.
YUI bears a striking resemblance to Backbone, perhaps due to being inspired by it. My extensive examination of Backbone has left me impressed with its principles and standards. It encourages the development of a sturdy framework if adhered to diligently.
Interestingly, I came across a comment from someone who transitioned from Backbone to YUI citing the latter as more streamlined and superior overall. While I cannot confirm this claim yet, it warrants further investigation from my end.
Many individuals, myself included, argue that Ember, Knockback, and Angular have a somewhat heavy-handed approach. They prioritize explaining HTML interfacing from the outset, which may either pose challenges or simplify tasks depending on one's specific project requirements.
This is simply my viewpoint based on personal observations and experiences!