Wow, didn't realize there were so many ragged right fans. Makes sense based on Kovid's point about larger font sizes, but I'll stick with my personal preference for justified text.
I feel similarly to Kiwidude about keeping things similar to printed books - but I guess this indicates Quality Check may need the opposite check for everyone else.
Agree that things like kerning and smart hyphenation would also help a lot for either scenario, that's more a software/epub spec problem, another I wish would get solved...