Just like frequent flyer programs, the alliance you marry into can affect your airport experience, how you earn or burn miles and even where you take your hard-earned vacations.

One of the first steps in the journey toward true frequent-flyer-dom is choosing one or two airline frequent flyer programmes and remaining loyal to them to earn miles and enjoy the resulting perks, such as upgrades or access to shorter lines.

But few travellers have a true “choice” among airline programmes. That decision largely depends on which airline dominates their hometown airport and which destinations they fly to most often. For business travellers, the decision could be made by employers, which may have negotiated special discounts and mandate the use of a specific carrier or one of the three global airline alliances: Oneworld, SkyTeam and Star Alliance.

But given the choice, loyalty to one or two carriers eventually pays off in the form of entrance into the hallowed halls of airline “elite” status, granting an array of valuable perks at your chosen airline. But what may be even more important to global travellers is that these benefits extend to the carriers’ alliance partners around the world.

For example, imagine you are a member of United’s US-based Mileage Plus plan and you would like to redeem miles for a honeymoon trip to Santorini in the Greek Isles. Without an alliance, you could use your miles to fly as far as London or Frankfurt, and then you would have to buy a ticket on another airline to get to Santorini. But since Lufthansa is a member of the Star Alliance, as is United, your ticket redeemed with miles could include the leg from Frankfurt to Athens. And since Greece’s Aegean Airlines is also a Star Alliance partner, you could add on the short flight from Athens to Santorini. The reverse holds true for a member of Aegean’s Miles & Bonus plan who may want to travel to the US.

“You may have heard the adage ‘Marry the girl or the boy, but you end up marrying the family’ — the same holds true when choosing an airline and its alliances,” said Henry Harteveldt, the travel industry analyst for the Atmosphere Research Group in the US.

Just like the airline you choose, the alliance you marry into is an increasingly important factor that can affect your airport experience, your ability to upgrade, your ability to earn treasured airline elite status, the ease with which you earn or burn frequent flyer miles, the price you pay for your tickets — and even where you take your hard-earned vacations.

“Like frequent flyer programs, the ‘best’ global alliance is the alliance that works best for you, given your travel patterns,” said Tim Winship, editor of FrequentFlier.com. “As tie-breakers, first would be coverage [number of cities served], second would be the quality of the partner airlines.”

To help you find the one that works best for you, here is a primer on the world’s three global alliances, listed below in alphabetical order:

Among the three global alliances, Oneworld is the smallest in terms of number of member airlines (12) and number of destinations (766). But for what it lacks in quantity, it makes up for in quality with major players that fly to iconic business travel destinations, such as London, New York, Tokyo, Sydney and Hong Kong.

Larger members include American Airlines in the US, British Airways/Iberia in Europe, Qantas in Australia, LAN in South America and both Japan Airlines and Cathay Pacific in Asia. Smaller member carriers include Finnair, Hungary’s Malev, Royal Jordanian and Russia’s S7 Airlines.

Oneworld recently decided to bring India’s Kingfisher Airlines into the fold, filling a major gap in its global coverage. However, the revelation of the carrier’s severe financial difficulties could delay its admittance, and prolong the pain caused by missing a partner in a key growth market like India. The alliance also lacks significant coverage in Africa.

One key benefit of Oneworld is that top tier, elite level frequent flyers from member airlines (typically those who fly more than 50,000 miles per year) get Sapphire or Emerald tier status in the alliance, which provides access to 506 airline lounges around the world, regardless of class of travel. Even if you fly in economy, you will still have access to some of the finest airport lounges in the world — such as British Airway’s Galleries at Heathrow’s Terminal 5 in London, Qantas’ first and business class lounges in Sydney, and Cathay Pacific’s award winning lounges at the Hong Kong International Airport.

strong points lie mainly in the size and strength of its founding members: Delta Air Lines — the second largest carrier in the US after United, with hubs in key cities like Atlanta and New York —  Air France/KLM —  the largest airline in Europe, operating out of Amsterdam and Paris — and Korean Air’s excellent hub in Seoul for travel across Asia.

With the recent admittance of China Eastern, China Southern, China Airlines (Taiwan), and soon, Xiamen Airlines, SkyTeam is the clear alliance winner in the increasingly important Chinese air travel market.

Other prominent SkyTeam members are Russia’s Aeroflot, Spain’s Air Europa, Italy’s Alitalia, CSA Czech Airlines, Kenya Airways, Romania’s Tarom and Vietnam Airlines.

The alliance’s 15 members fly to 916 destinations around the world, making SkyTeam the second largest of the three. Like Oneworld, SkyTeam lacks a significant partner in India, and its coverage in Latin America remains sparse compared to other alliances. With Kenya Airlines onboard, SkyTeam covers more than 40 destinations in Africa.

International first, business and SkyTeam Elite Plus members (those at the top of the elite tiers at member airlines, typically flying more than 50,000 miles per year) have access to 490 SkyTeam lounges around the world. Over the last two years, the alliance has grouped all SkyTeam member airlines in single terminals at London Heathrow Terminal 4, Barcelona Terminal 1 and Moscow Sheremetyevo Terminal D. The move eliminates the hassle of transferring between terminals to visit lounges or catch flights on partner carriers, offering a truly seamless travel experience, which is something alliances like to promote, but are not always able to deliver.

Star Alliance
Created in 1997, Star Alliance was the first and remains the largest alliance in terms of member carriers (27) and destinations served (1,185).

Key members include several of the world’s largest and most highly regarded airlines in key regions. North America is blanketed by coverage from Air Canada, Continental, United and US Airways. Europe is anchored by Lufthansa’s giant hub at Frankfurt, plus the United Kingdom’s BMI, and Swiss, Austrian and SAS airlines. South African Airways covers most of Africa. Oceania is covered by Air New Zealand. In South America there is Brazil’s largest carrier, TAM. In Asia, members include some of the best airlines in the world: Singapore Airlines, ANA, Thai and Air China. South American carriers Avianca (Colombia) and Copa (Panama) will join the Star Alliance in 2012, which should help fill in gaps in Latin American coverage.

Among most industry observers, the Star Alliance is the clear leader of the pack. “Firstly, Star was able to snatch up some of the world's premium airlines into its fold early on,” said writer Ramsey Qubein, who covers airline alliances for several publications. “Secondly, with 27 carriers as partners, the entire world is at your fingertips. Thirdly, the benefits for frequent travellers include lounge access, increased baggage allowances, and priority check-in for Star Alliance Gold members. While all alliances offer similar benefits, Star offers them on more airlines and in more cities giving it the unquestioned upper hand.”

Business, first class and Star Alliance Gold customers (those at the upper end of elite status with the airline program they fly most) have access to 970 member airline lounges, as well as dedicated Star Alliance lounges at London-Heathrow, Los Angeles International Airport, Nagoya-Chūbu Centrair and Paris-Charles de Gaulle.

To help ease the way for connecting travellers, the alliance has adopted a “Move Under One Roof” initiative that takes on the expensive and time consuming task of shifting all member airlines into single airport terminals, which makes transfers and lounge access more seamless. All Star Alliance airlines are now under one roof at airports in Bangkok, Beijing, Miami, Tokyo-Narita, Seoul and Singapore. 

The downsides
While airlines are keen to promote the positives of these alliances, there are negatives. Airline frequent flyer programs, seating, aircraft and computer systems vary widely from airline to airline, which can make redeeming miles or points across programs, or even gaining access to far-flung airport lounges, inconsistent and frustrating. Similar to translating languages or exchanging currency, travellers may experience gains or losses since no two programs are exactly alike. Also, when airlines join together to set schedules and fares and jointly market themselves, it tends to stifle competition, which can ultimately lead to higher prices.

Not all airlines around the world play the alliance game — notable exceptions include the United Kingdom’s Virgin Atlantic and Emirates in the UAE, as well as many rapidly expanding low-fare carriers such as Southwest and JetBlue in the US, and EasyJet and Ryanair in Europe. So staying loyal to your frequent flyer program might not always lead to the greatest savings.

Chris McGinnis is the business travel columnist for BBC Travel