Ravers love rainbows.  It's hard to beat a smooth animated bright rainbow pattern -- it goes with everything. 

We've included two different ways to program your LEDs: Arduino or CircuitPython.

Which one should I choose?

There are pros and cons for each method.  At the time of writing, CircuitPython is still a brand new thing, while Arduino is a bit more tried and true.  Both will work to make pretty rainbows!

The Arduino IDE currently has way more code samples and control options available.  If you're excited about tweaking the code to get it just right, and building on code samples posted by other makers, you may want to stick with Arduino for now.  It takes a few steps to get everything installed, but you only need to go through the process once.

CircuitPython is exciting because it's easy to set up and easy to use.  Many people already know how to code in Python, and it's just a short step from Python to CircuitPython.   There are fewer steps -- not so much to install, and you don't need to compile and upload the code every time.  Instead, the Gemma M0 will show up as a drive on your computer and you can just save files directly to it.  But at the moment, there aren't yet a zillion open-source samples on the internet just waiting for you to download and try.