I like blender personally
I personally do not understand the need for CAD in IQ. It is so quick to snap parts together there is really no need besides to add a little spice to your notebook in my opinion.
You are right that CAD may seem like a waste of time in VEX IQ due to how (relatively) easy it is to rebuild in VEX IQ. However, CAD is helpful in VEX V5 (for those who intend to move on to VEX V5 after VEX IQ) and is also a great skill to develop due to its use in countless engineering jobs.
Completely agree, cadding V5 is very useful.
Try Snapcad. It is free, and you only have to download one thing, because the part libraries are included with the app. Here is the link to the download instructions:
Snapcad