I have always chosen knocking up the LIs when a VN offers that path.
I would like to see a heavy romance story VN go further and follow through on the relationship of parenting from birth onward. Not involving the kids in incest .. but a loving couple (or harem) raising kids well.
Yes, if I have the option, I always do it. Curiosity is stronger, and I also like seeing the changes that happen during pregnancy and the new options it could bring.
I like "impregnation," the emotional ramifications of it, and the effect it can have on the story, but not so much "pregnant sex." So yes, unless there's going to be a timeskip mid-game that leads to actual pregnant content. Kids or pregnant LIs in the epilogue are nice, though.