One of the best emulators that will find for free is "Google Chrome". Simply go to Tools - Developers Tools. Click on the small mobile icon present on the left side.
You can also open developers tools using Cmd + Shift + I or Ctrl + Shift + I.
Using this emulation tool, you can test your design for almost all types of mobile devices. It also has features like Network throttling that lets your see how your website loads in slower networks.
I hope this helps. :)
My day starts with localhost and an espresso.