How do you decide which software to choose for designing i always get confused while selecting the software.
I usually use solidworks because of better user interface.
what are the criteria on which you judge.
It depends on what you are designing, what software you have available, and how well you know the program(s).
I use SolidWorks as it just about the only CAD program I've used in years.
If you put a dozen new programs in front of me, I'd still use SolidWorks, simply because I know how to use it.
The exception would be if the design required shapes, or functionality which SolidWorks does not do well. Then I'd either not make the model, or I'd have to learn a new program.
I even use SolidWorks when I shouldn't. I know I should use Photoshop, or Illustrator to make simple signs around the office, but I often use SolidWorks for the task.
Since there is no program that can do anything, it's best to do everything with the program you love and that you will love for a long time. I took 3 months to decide that I would learn 3d using Solidworks and I took several courses to have the manuals in hand and do all the exercises, all that remained to practice. I never regretted my choice. Now I go regularly to Youtube when I need to model what I have not yet learned.