Depends on what you mean by best. You might prioritize individual freedom, social mobility, economic and military powers, population quality of life, etc.
Here is my opinion on different government types. Efficiency here stands for the ability of the government type to take effective action.
Autocracy: Will collapse or face turmoil with the loss of the leader. One person is also not enough to direct too many operations. Will exploit a portion of the population either for the good of the many, or the good of the leader. Extremely efficient on a smaller scale and with a good leader, but with problems scaling up due to lack of continuity and .
Democracy: Individuals can attempt to maintain rights and fight exploitation. Inefficient do to the massive number of competing interests, an individuals inability to be informed on all decisions while maintaining a regular life. Extremely vulnerable to misinformation because of the number of things an individual must make an informed decision on and lack of resources to help them.
Oligarchy: More stable than an autocracy and allows for more operations. Will eventually lead to exploitation of the population just like an Autocracy. Very efficient with good leadership, however it will face rebellion once the ruling class get to far out of touch and/or exploit to heavily the population.
Republic: No guarantee that the representative will work in the best interests of the individuals he represents eventually leading into oligarchy. Slightly more accountable as people know exactly who is supposed to be helping them and doesn't. Less efficient than an oligarchy as representatives focus on their specific domains sometimes at the expense of the whole.
Democratic Republic: Voters can hold their representatives accountable if they do not work in their best interests, and can pick the representative that they feel is best for them by vote. This allows them to fight against exploitation and maintain their rights via their representative vote. Less vulnerable to disinformation than a democracy because of less choices and more focus (on the representatives themselves) but still vulnerable. Vulnerable to large political organisations limiting who can potentially be a representative combined with voter complacency or disinformation so that representatives are not held accountable, leading to a Republic and eventually Oligarchy. Less efficient than a republic as representatives must continually appeal to their constituents to maintain their position, but still more efficient than a pure democracy as representatives do not maintain a regular work life and have more information sources with a better ability to compromise.