Question does not contain criteria for 'Best' :) If you ask me about simple - here is one: JS Miinifyer (http://jscompress.com/)
- This is simple - copy paste your JS and get the output.
- This checks syntax - it will not compress if there are syntax errors (at least some level of checking I am not sure if it checks details.)
- You can upload JS files also instead of just copy paste.
We used this for our productions deployments to do: 1. Compression. 2. Uglify JS