Ask HN: How do you design UI applications?

I recently built a basic GUI application to help with the chore of selecting photos for wedding album prints from a digital collection. The app merely saves the names of photos that the user selects (/likes). I used tKinter in PY. A few of my friends were also interested, but I found that my app wasn't robust enough. I am curious to know what language/GUI programming paradigm is easy to learn for beginners and yields good robust solutions. I just started to look at QT which seems to support cross-platform. Please advise :).