Python or JavaScript for Practice: which do you use, and why?

Practice runs both Python and JavaScript. Which do you use, and why?

Some things I would like to compare:

• Did you pick the language you already know, or the one you want to learn?
• Which makes the problems feel easier? Python's built-ins often shorten things, JavaScript's quirks (==, type coercion) sometimes bite.
• Has anyone solved the same problem in both? Did it change how you thought about it?

If you are unsure which to start with, tell us your goal and we will suggest one.