My favorite save is the one I started when I got Get To Work.
I started with a Single Sim called Erik Tuuli. He became a scientist and it was so much fun to play. He met an alien woman at work and they had a short relationship which lead to her getting pregnant and having twins. I found out later that she had "hates children" trait and I didn't want her to be Erik's wife, so they broke up. The children stayed with their mom, but Erik visited them often and vice versa.
Later Erik met Summer Holiday and she became his wife and they had a daughter, Emilia. Emilia became a painter and married Alexander Goth. They have two children, Ville and Annina. Ville is still a child and Annina is a toddler (she's alien, Alexander was kidnapped and became pregnant). Alex is a freelance writer.
Erik's half alien twins Juho and Venla are both married too and they have children, so Erik has 4 grandchildren in all. Emilia and her family are living in the same house than Erik and Summer in Willow Creek. Juho and Venla are living elsewhere with their families.
Erik is my favorite Sim ever. I've given him (and Summer also) two youth potions already, because I don't want him to age up to an elder. I love his personality, I have never had a Sim who feels like a real person more than him. He has reached the top of his career a long time ago and so has Summer (she is an athlete).
I love this family and I can't wait for Erik's grandchildren to grow up and see how they look like and choose careers for them etc. I have aging on long and I think I'll give Erik and Summer one more youth potions both and then I let them age up finally.