Of course, you want your kids to have lots of love. You want them raised with the values to which you adhere. And their education is likely very, very important to you. Then list all the people who you think could likely fulfill these wishes. Parents, siblings and beloved friends will probably all appear on the list.
Religious heritage is very, very important to many people.
If you are a devout Orthodox Jew, you may not want your child raised by a Catholic best friend. Sure, you may have enough money to financially care for your kids after your death. You do not want your kids to become an undue financial burden on their new guardians. You do not want your children raised in an atmosphere of resentment. Determine which of your child's potential guardians embrace a moral code you respect.