It's really quite relative. There are so many good IDEs, but each is a little different. Here are a few to try out:
NINJA-IDE: My personal favorite Python IDE. However, it is temporarily incompatible with Ubuntu 17.04+, since they're still depending on Qt4 (which was DC'd on 17.04 onward). However, it works VERY well on any system that Qt4 can be installed on.
Atom: My current IDE. It supports many languages, Python being one of them. If you install the packages for the Python language syntax, linters, autocomplete, and debugger, it makes for a fantastic interface. However, I use the Terminal for running the Python code when using Atom.
Spyder: One of my employees was first introduced to coding via Matlab, so I suggested Spyder for him (due to its interface similiarity). As far as I know, he's still using it.
There are plenty more besides, but those three are at the top of my list. They're also all open source.
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