Which TVD fanfictions should I write?

I am planning some Steferine fanfictions but I don't know which idea if the best and which to start écriture first. Help me?

1. "Why do I still feel you?"
Stefan and Elena are happy marriage couple, all they need to be plus happy is a baby. Davina knows the spell cause of which it can happen, but there is one thing- mother has to be human. How will it change Stefan's feelings for Katherine and Elena?

2. "An old flame"
Katherine in Elena's body comes to Stefan and says it's her not real Elena. What's gonna happen? (oneshot ou more)

3. "The best memory"
What if Damon didn't give Katherine the memory of the death of her entire family and Stefan will be the one to see her best memory on her death bed?

4. "The broken ones" Elijah betrayed Katherine, Elena betrayed Stefan. Will brokenhearts pull hurt ones closer?