React, Angular, Polymer all let you build powerful websites. React and Angular are already successful now and would be safe bets. Polymer's success was in question in the last year because unlike the other frameworks it was contingent on Apple and Microsoft agreeing in a particular vision(web components). but MS and Apple are coming along now, just slowly. So if you're really attracted to Polymer's vision and you're willing to tolerate a little API turbulence and significant portion of your development will be in the next year or so, Polymer would be a great choice.