I did a wee bit of time with Tkinter 15 years ago, then a few years later I did something with wx. While I was able to get stuff done, I found them a both a bit tedious. I don't know how much the situation has improved since I last used them -- or how much my own learning would make them seem easier today.
However, in the past few months, I've been exploring PySide, which is a PyQt-compatible framework. Incredibly useful is the Qt Designer, which allows you to drag and drop components (push buttons, dials, sliders, checkboxes, etc.) and save them as an XML file with the extension ".ui". pyside-uic then reads that and produces Python code. There are some GREAT tutorial videos out there.
Bo Milanovich has a 29-video series on Udemy (for $15) which I just completed, but also has several free of cost listed on the Qt site: http://wiki.qt.io/PySide_Video_Tutorials. Bo can be a bit "distracted" in his lessons, going off on tangents, but for 29 lessons averaging 30 minutes each, it was definitely worth $15.
I also recently found "Qt Designer - PyQt with Python GUI Programming tutorial" (https://www.youtube.com/watch?v=Dmo8eZG5I2w). That led me to the presenter's site which offers intros to Qt, Tkinter, and Kivy https://pythonprogramming.net/gui-development-tutorials/. I haven't watched them, but based on the Qt Designer tutorial that I did watch, I'm looking forward to the ones on pythonprogramming.net.
Some of the official PyQt and PySide documentation is a bit lacking. Much of it was converted via some automated process from the original Qt documentation, and bits were lost in translation. So, if the docs at https://pyside.github.io/docs/pyside/ are lacking, see the docs at http://doc.qt.io/ and try to translate what you read to Python. But watch the tutorials first, as they will take you a long way.
I briefly looked at GTK a few years ago. It also has a designer, glade. I considered going down that road again, but for the things I've been interested in, there seemed to be more energy behind Qt. I'm JUST starting to explore Kivy, as it seems to be recommended for touch screen work.
A bit late, but I hope this helps.