In the United States, the first-past-the-post system is employed for presidential elections. Under this system, the candidate who receives the most votes, even if it's not a majority, wins the election.

The first-past-the-post system guarantees a clear winner, even if no candidate receives a majority of votes. This simplicity and decisiveness are often seen as advantages.

Ranked-choice voting enables voters to rank candidates in their order of preference. If no candidate receives a majority of first-choice votes, the candidate with the fewest first-choice votes is eliminated, and their votes are redistributed to the remaining candidates based on voters' second-choice preferences.

Ranked-choice voting eliminates the need for a runoff election by allowing voters to express their preferences for multiple candidates. This can save time and resources, and it can also help to ensure that the winner has the support of a majority of voters.

Proportional representation is a voting system that aims to ensure that political parties are represented in proportion to their share of the popular vote. This is achieved by dividing the country into electoral districts and allocating seats in the legislature based on the number of votes each party receives in each district.

The main advantage of proportional representation is that it facilitates proportional representation, meaning that political parties are represented in the legislature in proportion to their share of the popular vote. This can lead to a more diverse and representative legislature.

The two-round system involves holding two rounds of elections to determine the winner. In the first round, voters cast their ballots for their preferred candidate. If no candidate receives a majority of votes, the top two candidates advance to a second round, where voters choose between them.

The main advantage of the two-round system is that it ensures a clear winner, even if no candidate receives a majority of votes in the first round. This can help to prevent prolonged political instability and uncertainty.

The single transferable vote (STV) is a voting system often used in local elections and for selecting party candidates. Under STV, voters rank candidates in order of preference. Votes are then transferred from lower-ranked candidates to higher-ranked candidates until a certain number of candidates have reached a quota of votes and are elected.

The main advantage of the single transferable vote is that it promotes consensus among voters by allowing them to express their preferences for multiple candidates. This can lead to a more representative and inclusive outcome.

Approval voting is a voting system designed to prevent strategic voting and ensure that voters' preferences are accurately reflected in the election results. Under approval voting, voters can vote for as many candidates as they approve of, and the candidate with the most votes wins.

The main advantage of approval voting is that it eliminates the spoiler effect, which occurs when a third-party candidate draws votes away from the two major candidates, potentially causing the less popular of the two major candidates to win. Approval voting allows voters to support multiple candidates, reducing the impact of spoiler candidates.

The Condorcet method is a voting system used in Switzerland for electing the Federal Council. Under the Condorcet method, voters rank candidates in order of preference. The candidate who would defeat all other candidates in a head-to-head matchup is declared the winner.

The main advantage of the Condorcet method is that it ensures a clear winner who would defeat all other candidates in a head-to-head matchup. This can lead to a more legitimate and representative outcome.

The single transferable vote (STV) is used in Ireland for electing the President and members of the Seanad Éireann. Under STV, voters rank candidates in order of preference. Votes are then transferred from lower-ranked candidates to higher-ranked candidates until a certain number of candidates have reached a quota of votes and are elected.