How much effort do you want to put into this?

KiXtart + AutoIT is easy to get into and start scripting. You could have something up and running inside a few hours.

C++ has a very high learning curve. If you don't already know C++ or another object oriented language it is going to be days before you have even the basics of your project working, and debugging / enhancing it will take longer.

On the other hand, KiXtart cannot perform all the tasks that C++ can. It simply doesn't have the ability to handle certain data types or call the same APIs that C++ can.

To select the right language you must start by determining your final goal.

If your project is as simple as reading a graphical object, detecting a mouse click then clicking on a button then KiXtart + AutoIT will be fine.