I wanted something with not that much features so I can learn it.
Codea has a marginally easier entry - but to do anything more complex than a simple demo, you will need to get deeper into the language than you might think, and Python is (IMHO) no harder than lua. Pythonista itself is a bit harder to use to make a graphical demo, but not much harder, and there are things you can do in Pythonista that are not exposed or possible in Codea.
So - if your goal is to make fun things on the ipad, either will work. If you want to learn, you will find the concepts in Pythonista carry on out to other environments, but much of what you learn in Codea is the Codea libraries, not lua, and is not easy to take out of there. (The closest analog outside of the ipad is probably love2d, you can google for it)