Depending on your system I think, I have been using Sketchup 2017 (whatever the last free version was they released) for years to make 3D models for all kinds of purposes, incl 3D printing. For my brain it has proven to be the most intuitive tool to learn, it’s been a really long time so maybe I have forgotten but I feel like the barrier to entry was pretty small. There is a lot of content out there from people giving tips and tutorials. There are plug-ins still flooding around that have really good functionality. I use it with a Connexion 3D Space Navigator mouse that’s prob 10+ years old. That’s been a godsend and adds so much efficiency and flow to the tool.

I don’t know if you can still download it from Trimble but there are sources for it elsewhere.

Have fun, whatever you choose.