I've been heavily leaning towards Cycle.JS lately (http://cycle.js.org) for personal projects. I haven't pushed anything to a Production environment yet, but I really love Cycle a lot more than React. (Cycle is vaguely like React, and explores some similar goals, but Cycle is based on RX and encourages a stronger, immutable functional composition than React.)

For production applications at the moment I'm still mostly using Knockout as it is reliable and runs almost everywhere.