I chose three:
Economy and taxation
I think they are almost symbiotic in nature.
Economy is necessary for a country's overall well-being. If you don't have a stable economy, everything else is eventually going to suffer from it. Of course, you also need taxes to fund basic public services, build and maintain infrastructures, etc..
Healthcare is also very important. To me, it's a necessity. Without proper healthcare, people die. It's that simple. Any civilized country should be able to take care of people who require health-related services. My opinion, concerning healthcare, is that there are no compromises.
Third, and not necessarily least; education. Education represents the future of any country. Your people need to learn as much as possible in order to maintain your country's competitivity. The students of today will one day be those who will be in charge. It's up for any country to make sure they are taught the right things, and it should also be important to lower the costs of education so that the students can reach college and university without being crippled by lack of money and debt.