https://www.wunderlist.com/en/
After trying probably 30 different todo list apps over the last 3 years, I recently settled in on this one. For me it's the perfect collection of features with ease of use, and built from the ground up for mobile use. Others I tried were too simple or more often, way too complicated w/ cluttered UIs. I just like have a few different types of lists of stuff I can check off.