I have many clients with small children, and almost universally, the reason they say for why they took so long getting their wills done is that they simply couldn’t decide on a guardian.
If you have children under 18 when you die, ultimately, it is up to the courts as to who will become their guardian. However, if you have named someone in your will, that will carry significant weight in the event of a challenge from someone else. Also, only people with standing can apply if you haven’t named anyone; sometimes, a friend who lives in your city would be the best choice, but that friend would not have standing unless named in your will.
You will never find someone who shares identical parenting values and traits to you and your partner. That simply isn’t possible. The best you can do is a close approximation. The worst you can do is nothing.