I've tried a lot of 3D software over the years, and OpenSCAD has been the one I've been most successful with (along w/ Carbide Create, but I work for that company....)

Currently working on a library which makes the two work together:

https://github.com/WillAdams/gcodepreview

(which is currently quite primitive/basic, and even when fully developed is not likely to be used by anyone else)