I think Sims with strong personalities are memorable. I don't care about what they look like, it's all about the personality and their expressions while they're doing their things.
My favorite Sim Erik Tuuli is a very proud Sim, he always walks confident walk and he doesn't like anyone being mischievous with him, he gets very angry. His oldest kids got to know his rage when they were children and tried to trick him. He was furious. However... his dark secret has always been that he himself loves trolling the forums. He's doing it a lot when he has free time and he's very excited about it. Maybe a bit too much sometimes.
Another one of his passions is playing the violin wearing his underwear. Most times when he plays the violin, he's on his underwear, he just wakes up, walks downstairs and starts playing. His sleeping schedule is weird and it's hilarious sometimes when the rest of the family (and sometimes they even have guests) is having a dinner and suddenly I hear violin... Erik wearing his underwear is playing the violin in the living room.
He's deeply in love with his wife, Summer Holiday, they've woohoo'd autonomously several times. He also spends a lot of time with his grandkids, he can deal with toddler tantrums, but not mischief.
When I started playing with him back in 2015 he got to know Mortimer Goth who came to see Erik every day the same time. Erik is a scientist and he sat down to eat after his work and every day Mortimer knocked on the door the same time. They talked a lot and soon they became best friends. When Erik got married he didn't have time for Mortimer anymore and I feel very bad about it. He came knocking on the door religiously every day and Erik ignored him until he gave up. Erik's daughter ended up marrying Alexander Goth and I felt bad when Mortimer suddenly died. I don't even remember seeing him as an elder many times.