[egeozcan]

My choice is React.js

Time needed: I'm not sure. Rendering something on screen, including setting-up the environment, took an hour, tops. But with all the surrounding terminology and concepts, it may have taken around a week or two as I had just the afternoons. I think around 20 hours of investment would bring you good understanding of how React.js works, accomplishing the boring stuff with it like routing and state-management with something like Flux, understanding how to render from server and share code with the client.

Development speed: 1 in the project startup, with an exponential speed increase towards 3 as complexity increases, all relative to Knockout.js and Angular.js.

Maintainability: 3. I think this is where React.js shines. If you apply the common design patterns that are popular among many React.js projects, you'll be guided to write maintainable code and your data will flow in a single direction. I can't overstate the burden this removes when you are developing a complex application. Strange things never happen.

Why: I try all the frameworks and experiment with them just for the fun of it. I stayed with React.js because it made things easier to maintain, as stated above. Development speed wasn't so attractive in the beginning but later, after finishing a project or two, you get on par with the alternatives.