I do a mix of everything I guess? I usually start exclusively with a rags to riches challenge, then I morph it into a sort of random legacy challenge - where traits are randomized and so is their aspiration but I don't randomly choose how many kids they're going to have or their marriage state. I just kind of let the story play out - like my current founder had two children in Akita Kibo despite him being married (at the time) to Mila, but he also had a kid with Nancy Landgraab lol. This is the furthest I have gotten in a Sims 4 legacy but I plan on using the spares for each generation and doing other challenges, like I might use Levi for a 7 toddler challenge or I might decide Laurie is the spare and use her for a 100 baby challenge or something, curious to see how it's going to go in all honesty.