My favourite save is the very first save file I started back in August 2015. I've played with majority of the premade households and fleshed out their stories with each other and my own sims. I've established a headcannon and refused to allow the world to age until certainly milestones have been completed. So it goes without saying that I play with aging off. In addition I have just around 200 sims I actively play with and around 50 not in world sims that are integral to individual stories. Because I heavily micromanage this save I try not to allow too many bizarre townies about, but if encountered they will either be edited in cas or swapped out with unique sims from the gallery.
The biggest concern I've encountered in this save is from manually aging up my sims. Some teenage sims have been born into the world and gone through their birthdays while others have been that age or close to from the start. I'm trying to figure out in my head what should be the proper age of all my sims at this point before I turn aging back on. Yeah. Pretty much my goal is to one day have aging turned back on with MCCC story progression when I'm satisfied with where all my sims and the premades are at. Then I could focus solely on my absolute favourite households.
The 2015 save file is my most precious, but since its creation I have created and lost a number of save files that I throughly enjoyed like my K-pop world, Not So Berry Challenge, and a Prison Challenge which utilizes the save file from Lilsimsie.