Democracy is one of the best because it has a lot of advantages like; its protects the say and interest of people, it prevents dictatorship, it makes everyone have equal rights in the country, it makes the government closer to the people, and many other advantages which makes people happy.
Throughout time, many nations have had different governments, but democracy has come out ahead. If you compare democratic governments to non-democratic, governments have had a very long lifespan. There have also been a lot less internal conflict within the countries, because if the leader is not liked he will be voted out instead of there being a war for a change of power.
The best form of government depends a lot on the the people and state being governed. In a unified and developed nation with a high degree of education, democracy has generally proven to be the best government. In a country that is highly fractured along religious and ethnic lines and/or where literacy an education are low, democracy can be disastrous. I think history has generally proven this.