Unfortunately there aren't a whole lot of good options. They're either commercial and therefore potentially cost $$$ (or are time limited or otherwise restricted), or they're free and kind of suck in one way or another.

Of the commercial offerings I like OnShape. I think Fusion 360 is fine too. They're WAY more powerful than anyone needs for just designing 3D parts but they're still powerful, well designed tools. I think if your needs are simple and you don't care a great deal about complex shapes then Tinkercad is great too.

Of the opensource, FreeCAD is the closest to OnShape / Fusion 360. It's a parametric modeller like they are but the user interface that throws every button in your face at once and doesn't bother to sort them very well or provide context. It's not an intuitive or forgiving tool and really needs a usability makeover to make it as simple as the commercial equivalents. I've never had much success with it because of this.

Blender is pretty popular for modelling. It's not really CAD so it's likely more useful for modelling free form / artistic stuff. The UI is pretty complex but it is extremely powerful.

OpenSCAD is pretty neat if you want to create something by essentially programming a shape and rendering it. It works well for certain kinds of geometric designs that are better expressed in code. e.g. maybe you have to punch 100 holes in a spiral pattern on the side of a box or something.