Technically, there’s no “Christian country” in this era because the religion adheres to separation of church and state, unlike Islam where we can find many theocracies.

But, to call a list of successful democracies where the majority identify as Christians of some sort and without colonialism in its past;

Norway

Switzerland

Denmark

Liechtenstein

Oh, Sweden too.

And it’s funny why you specifically mentioned without past colonialism and genocide, because many Muslim countries score high in this sector too.

Sweden had colonies in north America and the Caribbean. Denmark still controls Greenland. Sweden and Norway are both colonizers in the US way, expanding boarders by stealing land from the indigenous people (Sami) etc

Unlike the Islamic countries that live eternally peacefully with their neighbors I guess..not slaughtering each other like barbarians.