Day 01 - The first time you ever saw Superman Day 02 - When you became a Superman fan Day 03 - Your favorite Superman medium Day 04 - Your favorite Superman comic/title.
Wow, um...It really depends on who is writing or drawing the comic at the time. I guess my favorite title would be Superman/Batman even though it's been suspect since Michael Green stopped writing (I really loved the "K" arc, the Little Leaguers story broke my heart, and "The Fathers" just hit on all of my Clark/Bruce slashy love) . But the stories by Jeph Loeb (Public Enemies, Supergirl, Absolute Power) and then Michael Green are still high enough on my list that S/B remains a favorite. But obviously I still love Action Comics (Geoff Johns resurrected it with his LoSH* story) and Superman (though on the WoNK** front, Superman was better than Action, but that's because I loved how Mon-El was written and there seemed to be more of a resonance of Superman's influence than in Action Comics).
*Legion of Superheroes
**World of New Krypton
The Rest of the Meme Questions are Here