This is really hard because I have so many themed saves and when I'm enjoying them they are my favorite.
In the last few days I've played in some of my favorite repeat visit saves.
My Stardew Valley save based on that game/characters.. is a definite favorite because it's very cartoonish and melds with the sims gameplay so well. I can talk about it freely on the forums also.. lol. I can expand on the game it's based off of character wise... and play out situations I imagine could happen with the characters the way they were set up... and come close to representing them fairly well as well as expand on what they could be. I'm looking forward to ROM for two characters and hoping we get farming one day for another.
I just went into my Hannibal save and reset up some minor characters I hadn't gotten around to updating in that game and I'm off to play Freddie Lounds since we have more in depth photography in the game. I don't think I'll be leaving this save for awhile, because I decided she would investigate Strangerville while doing other things. I'm happy I have more tools without needing mods/cc to expand on her and play her out better in the game. I actually haven't played out Jack Crawford either and now he can become this games version of an FBI agent, so I gotta go that route.
I have a mannequin save where I've basically been color coding families and naming them in ways that reflect their colors like Coco and Cadbury Chocolate for instance. It really amuses to play dress up with them and I love the kind of creepy vibe I get when playing them. It's fun to go in there and not really have a goal or story but still feel like it's got some cohesiveness to it. It's like a quick but tasty snack of a save.
I do have many other saves that I return to though... and might bring up more later. As I said they are my favorites while playing them.