Well, by best, I mean in terms of providing visa-free access (although you can see a discussion regarding stylistic and aesthetic appeal here).
As seasoned travellers know better than anyone, certain countries require you to obtain a visa in order to enter; this document is separate from a passport, which is issued by governments to certify the identity and nationality of an individual for international travel.
Thus, the most convenient and desirable passports are those that do not necessitate a visa for permission to enter another country; in essence, the nation that the passport represents has special privileges to come and go without needing to obtain any additional documents (the difficulty or ease of which varies from government to government)
Here is a brief breakdown of the results by the Washington Post (Note that there are a total of 193 recognized countries (not including a dozen or so entities whose sovereignty or recognized independence is disputed):
The ranking puts the U.S. and U.K. passports first, giving access to 147 countries without an advanced visa. France, South Korea and Germany are second, with access to 145 countries, followed by Italy and Sweden in third; Denmark, Singapore, Finland, Japan, Luxembourg and the Netherlands in fourth; and Switzerland in fifth.
Advanced economies dominate the top of the list. Hong Kong comes in at 11, while Argentina and Israel are ranked 16th. Brazil ranks 17th, Mexico 22nd, the Russian Federation 35th, and China 45th.
The least desirable passports according to this ranking are from the Solomon Islands, Myanmar, South Sudan, Sao Tome and Principe and the Palestinian Territories. They rank in 80th place, giving access to just 20 countries each without an advance visa.
Perhaps it is not surprising that countries with the most economic and diplomatic heft on the world stage have managed to provide their citizens with the easiest means to travel.
Indeed, as the Post observes, whether or not a country’s citizens need visas to travel says a lot about the state’s influence or international likeability.
Countries that are allies often offer each others’ citizens a quick visa on arrival. For countries that are not so friendly, a visitor may have to provide entry and exit information, a letter of invitation, and even list all of the clubs they belonged to in high school — as well as paying a hefty fee.
Indeed, it is not unusual for nationals of one country to seek the citizenship of another country, if only because it may help open door to other countries that might not otherwise be as accessible.
Aside from being a nifty guide, the Passport Index also has a nice aesthetic quality to it, as you can view what each passport looks like in terms of color and design. There is also something neat about organizing the world’s passports by color (red, green, blue, and black).