With nuclear weapons you know that getting all enemy weapons is a slim chance. So you aim for maximum destruction of the enemy.
If I had to decide on targets I would go for max destruction in terms of lives. In the initial impact and in the long term. So the biggest cities, nuclear power plants, water supply, food production.
As said when usi g this option I don't expect my people to survive as well.
With nukes, you gotta stop your nuclear armed opponent from killing you second, first.