Yes, the STM version is worth the extra money for most people because the “III” version does not have Image Stabilization. IS should be on every general purpose lens. It allows you to shoot hand held photos in low light with slower shutter speeds provided your subjects aren’t moving too much. (great for landscapes and architecture)

Here are more reasons why the STM is better than both the IS II and III versions:

1) STM AF is faster and quieter for both stills and Video

2) The front element does not rotate on the 18-55mm STM 

3) The STM version has a proper manual focus ring. 

4) The STM version has "Full Time Manual Focus" available 

5) The STM version uses a nice "petal" hood because the front element does not rotate

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/Om2Kq.jpg