So many JS frameworks, so little time

I have played around with a number of different emerging and established client side MV frameworks, but I really want to sink my teeth into one of them to learn inside out. Something that I can use in a variety of applications and that has the maturity that will let me confidently use in production, and the versatility to be able to adapt to a variety of different application requirements. So HN, got any recommendations? I'm not necessarily looking for one in particular, even a generally respectable stack works, just something that I can commit to and roll with. Thanks guys.