React has a bigger community, more hype, more tooling around it, better native mobile support and better support for automated testing. But if I had to pick my

React has a bigger community, more hype, more tooling around it, better native mobile support and better support for automated testing. But if I had to pick my favourite, I'd have to go with Polymer because: - It's simpler (fewer dependencies). - Declaring styling and layout is cleaner (it's easier to visualise a component's appearance and to modify it during debugging because layout and styling are kept separate from a component's behavior logic). When it comes to debugging, styling/layout issues almost always happen independently from behaviour issues so it makes sense to keep them separate in the source. - It works better with browsers' native development tools. - No need for a compile step (and associated complexity that comes with it as your app grows). It's not fair to pretend that React bypasses the DOM entirely. Ultimately, when the user clicks on a button, they are interacting with a DOM element, so the event still has to pass through the DOM layer. The DOM is still the API whether you like it or not.