I would consider preschool at Renaissance Montessori. I cannot speak of SEC but have heard negative comments regarding Sunshine from educators and parents alike and have made the decision not to enroll my children there.
As far as the DougCo preschools, I would ask around in your area for advice. I know it's a lottery where you list your top three preferred choices for placement and there is no guarantee you will your first choice or "home" school. FWIW-my older children went through DougCo and I was pleased with the instruction they received.
I would also consider Skyview Academy---new school with PreK-8 as it is on that side of town in Highlands Ranch near Quebec and C470. Visit skyviewacademy.org.
Best wishes.