I'd also say Blender is a good option (I'm all about free and open source software).
I can't say I've tried tried any of the AI generation tools for 3D models, but I'd assume that if you were to use them; gaining some knowledge in something like Blender would help you modify them and fix them up for your specific needs.
If you want to learn how to make 3D models, I'd recommend starting with "Box modeling"-tutorials, where you start with a box, slice into it, extrude shapes and reshape it. If you mix that with "mirroring" (only making half of a symmetrical model, then generating the other half, like it's placed next to a mirror); I think you'll have a pretty good starting point to learn the more complicated stuff in whatever 3d modeling software you choose.