Currently still using a 16GB 6s as my primary device cos I gave the iPhone 7 to my mom. Didn’t install facebook, using the web version. Using iCloud Photo Library and iCloud Drive to store documents. No games. Tweetbot, instagram, fb messenger and reddit for social. Some productivity apps. ProTube for YouTube. Spotify premium with about 15 songs downloaded. Left with about 2GB free space.
I’d say if you use cloud storage, maybe 32GB is enough? I don’t feel overly constrained at the moment but having more is definitely nice.