Haven’t really explored the Blue Boy Scout that much, but I loved For All Seasons. It was so wholesome. The scene with Lana and Clark flying together for the first time sticks with me to this day.
Another series I really like is Red Son. In that Elseworld’s series, you see a Superman born in the USSR instead of in the US. What’s really interesting is how much of the basic Superman story remains despite the change in setting. Comparing the reader’s own understanding of Supes to the Supes on the page creates a sense of cognitive dissonance that I find to be fascinating.
While it’s not a Superman story exclusively, DKR III presents the classic story of Kandor in an interesting way. Without giving too much away, I will say that the series puts Supes at odds with his Kryptonian heritage in a powerful way. I’d recommend it to both fans of The Dark Knight Returns and Superman. Pro-Tip, though: Skip DKII. It has some important elements to understand DKR II, but it’s nothing a good Wikipedia article can’t clear up. The book itself is borderline trash.