Which version is best one for Photoshop ?

The one that works best for what you do. You should have at least two version of Photoshop installed if you use the current version of Photoshop the next update may brake something you use. All versions of Photoshop have bugs. Most are not in areas everyone uses. Some never run into a bug other are bitten by several.  Adobe fix bugs in code that ever user use.  Some bug will never be fixed there are bugs in CS2 Photoshop version 9 that are still in version 21.2. The bugs in photoshop can be worked around. Photoshop is a powerful tool and there are many way to do something you want to do.  Still Adobe release too many bugs and keep changing  thing on users with out any notice which is very disruptive to users work.  You need to have an old version installed for your own protection.