To make sure that time is spent as effectively as possible, I have created this reference chart. Also, if any of it is unclear, check out my extended thoughts on these matters: https://docs.google.com/document/d/1qJ0ttx1fGLf6ufP25i8KFX5C9bXEY9iUP0zw9DpGS1U/edit
That's nice. I'll add that 99.99999% of engrams received turn out to be rares. Since the patch I can't reall the last time I saw a legendary from a TIGER, or WEEKLY/DAILY.