How Design Work Is Easier in CAD Softwares? Which one is the best?

With the proliferation of parametric modeling, nowadays there really isn't a 'best' CAD package. All of the frontrunners are very robust and straightforward to use. In my opinion, the major deciding factor is simply what you've been trained on. Another important point would be what application your employer or machine shop use in order to maximize compatibility. This is mainly due to the fact that even though the state of CAD software has grown significantly, the cross-compatibility between packages is still sorely lacking. While most software packages can import and export standard files (such as STEP or IGES) easily, cross-compatibility of parametric models is, quite frankly, abysmal. Most programs are starting to introduce feature recognition tools but there is still a lot of work to be done in that area.

All that being said, I prefer to use SolidWorks because that is what I have been trained in, but I also feel that ProE (now Creo) does a much better job with its simulation and analysis tools. For the most part, you really can't go wrong with whatever software package you choose.