How do you guys decide which sim is the heir of a legacy?

I would pick Elsa if I were you! She seems like her kids would be the prettiest no matter who she has them with.
I used to pick whoever was the most attractive, but then my sims always ended up looking the same and I got bored. Now I follow the firstborn rule! It makes genetics end up more interesting in my case and I get some cool looking heirs.