I have written some programs to screen stocks. Nothing that would actually place a trade but rather just to sort data in a manner that any other service could not provide. I have written in Java, Python, Qt.
Java:
It's been a years since I have used Java. I found it to be slow and require too many try/catch statements. The pre-made packages are always limited so I decided to move on. Also at the time I looked at bench make times for program languages and Java turned out to be the slowest. Also it seams to change with every release which is pretty much annually and you end up updating your code.
Python:
Going back to when I last looked at bench mark times, Python was in the middle of the list. You can build code pretty fast. Again I found it to be to slow. Also the pre-made library Matplotlib, in my opinion makes ugly unlegible charts.
Qt (c++ pre-made library)
The best so far and by far. I find it fast, lighten fast in comparison to other languages hence it is c++ based which means you will have to get familiar with pointers and header files and other characteristics of the c++ language. According the the bench mark times it was the fastest and so far for me it is! I did have to do some thinking in some situations but it wasn't the bad. Great charts, lots of GUI objects and listeners are very easy to work with once you get the hang of connecting signal and slots. Qt creator allows you to build your program visually. Qt Creator is a light, fast, simple, ergonomic programming environment. End of the day, Qt is the best I have found as far as stand alone apps go.
At the end of the day as someone else had posted it all comes down to experience. I have been programming for 16 years now off and on pretty much for my own purposes. As you gain experience you'll learn what works best for which situation. Experience is the key no so much the language.