Traceur is more complete. ESNext requires less overhead. For most Traceur features, if you want to run it in a browser, requires a rather large runtime. ESNex

Traceur is more complete. ESNext requires less overhead. For most Traceur features, if you want to run it in a browser, requires a rather large runtime. ESNext is more modular. You can use just some features which may or may not require a runtime. It just depends. Overall Traceur is "better". But ESNext is nice if you just want feature X and don't want the overhead of having to support everything.