Tinkercad is a great free online CAD editor but Blender is a way better offline alternative. Tinkercad is very easy to get started with understanding the fundamentals of 3d modelling but it’s limitations of number of designs and polygons is a deal breaker.
Blender is a great free and open source tool that has extremely powerful features and amazing functionality. It is cross platform and extremely well documented.
So here are my 5 reasons:
1. Blender is free and open source, Tinkercad kept changing things around me (moving buttons etc) and it got confusing.
2. Blender supports more file formats
3. Blender can provide high quality image renders
4. Blender can create objects with more polygons
5. Blender has documentation for doing complex tasks