I'm going to use 123D Design from AutoDesk. I chose it because it's free and also because a number of the YouTubers who built interesting projects used it, and it seemed reasonably approachable.

123D Circuits is created by Circuits.io and Autodesk. It allows you to create a virtual environment using breadboards, Arduinos, and plenty more.

This is why we’re particularly impressed with the project. [Aaron] was able to 3D scan the lenses using his camera phone and Autodesk’s 123D Catch software (free) to create the lens model!