There are so many GNU/Linux distributions because nobody is preventing you from taking the code and making your own.
Here's a thought: start with the ten most popular one on DistroWatch, do a little casual comparison, and settle on what seems most interesting to you. As a designer, probably nothing will suit you better than the Fedora Design Suite (a "spin" of Fedora).
Personally, I read about it, hear about it, maybe watch a video about it. And I ask about it, as well. What would be the best way to find out about the distribution you would want to use?
Choose one if it doesn't work. Choose another one to get the best one you need to try.
Choose life.