What is the best software for mechanical design that you have ever used?

some of the most commonly used and highly rated software for mechanical design include AutoCAD, SolidWorks and Catia

CATIA and Auto CAD my favorite software to make mechanical modeling.

for mechanical modelling i have used siemens solid edge ST3 , i have done modelling and also assembling using this software 

for mechanical design i have used autodesk inventor and Solidworks.

but Solidworks is the easiest to the beginners in mechanical design.

Sorry i am not mechanical specialist, i can't help on this matter 

Regards

Solidworks and CATIA are the best for mechanical design. Once you get to know solidworks perfectly, you won’t be in need to learn any other cad software package. Solidworks is still the standard at this point for mechanical engineer.

The bottom line is that in all cases SolidWorks is the leading platform, and maybe you need to practice a little on AutoCAD and you will be fine.