I would say give tkinter a pass. If you want a simple GUI toolkit to wet your feet with, try wxpython instead.
Pygame. Pygame is based on SDL which is a little dated. You can however get quite a lot out of it as long as you know what kind of things slow it down. It is relatively simple to code and you can make some pretty solid 2D games in it. It can also be used in conjunction with openGL, but this just means pygame creates the window and handles events. Learning openGL is a whole 'nother battle in itself.
Pyglet. Pyglet is built on top of openGL. This is a more modern way to approach 2d graphics programming these days. It involves using an API built for 3D and setting the camera in orthographic mode. The primary advantage of this is many more of the cpu intensive actions will instead be carried out by the graphics hardware. Pyglet provides a layer on top of openGL to ease the process a little bit, but there is a bit of a caveat. Many of the drawing functions provided by pyglet (at least to the best of my limited knowledge) are actually using the fixed function pipeline. This is an outdated technique in graphics programming and in fact, if you ask questions about using it in an openGL community, they will simply tell you you should be writing shaders instead (which is again, a whole new, completely different thing you need to learn).
For now my personal (and incidentally biased) advice to you is, stick with pygame for the moment. Write a complete game. Complete. Title screen; menu; game; highscores; any thing else you would expect the game to have. But... choose something simple. Maybe Tetris, Breakout, or Pacman. I would suggest you don't try to tackle a platformer right away as these are actually deceptively difficult.
My first (and sadly only) essentially complete game. Fairly recently recoded from scratch.Youtube videoDouble Cross source/exeMy Pygame samples.An excellent book on 3D graphics programming.