Ask HN: Recommended stack for mobile-first webapp

(Yes, I realise this isn't Stack Overflow, but a roundup of current experience and opinion would be good) It's amazing how many options there now are for JS frameworks: Angular, Ember, Backbone, React to name just the ones off the top of my head. I'm an experienced Ruby/Rails developer and I've done a fair amount of Javascript/jQuery whenever needed. I've got a project which is virtually mobile-only and I'd like it to be lightning fast and smooth. So my feeling is that API first and a Javascript driven front end is probably the way to go here, but I have no idea what's the current recommendation. I really want to be able to wrap the whole thing in Phonegap/similar later to get native apps up without wasting all my work. Imagine you were building Uber as a webapp - that's the functionality I need.