NEW YORK (TheStreet) -- Airline travel can involve unpleasant moments, from going through security to waiting out bad weather to watching thoughtless passengers with too much baggage.

One way airlines and airports can enhance the experience is by making terminals pleasant places to be.

These are multi-billion dollar projects that take many years, so they involve major bets on the economy. For airlines, it can be difficult to quantify the financial benefit, but it is easy to make the case that gorgeous terminals like American's (Stock Quote: AMR) Terminal Eight at New York's Kennedy Airport provide a competitive advantage, given that international travelers in the New York area have a broad array of choices.

Similarly, because it replaced an antiquated facility, JetBlue's (Stock Quote: JBLU) Terminal Five at JFK vastly eased baggage handling and passenger traffic flow, making the operation far more efficient.

Hub airports also complete with other airports for passengers who must connect, so Delta (Stock Quote: DAL) and United (Stock Quote: UAL) gain advantages from upgrades at Detroit and Houston.

Read on for our choices for the nation's four most beautiful airport terminals.

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American Airlines Terminal at Kennedy Airport

American opened its Kennedy terminal in August 2007. At an opening ceremony, CEO Gerard Arpey called the $1.3 billion terminal "one of the biggest, boldest and most expensive projects in American Airlines history." The airy, imposing structure has 65-foot ceilings, 84 staffed ticketing positions, three passenger lounges and 36 gates.

Today, American and American Eagle offer 117 daily departures from JFK, making it a relatively small hub in terms of departures. But 31 of the destinations are international. The cornerstone is New York-London/Heathrow service, which, during the day, is nearly hourly, given that American is now able to coordinate schedules and pricing with partner British Airways. Other international destinations include Paris, Rome, Madrid, Zurich, Brussels, Buenos Aires, Rio, and Tokyo-Narita, with Tokyo-Haneda service planned.

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JetBlue Terminal at Kennedy Airport

JetBlue opened its innovative $750 million Kennedy terminal in October 2008. It includes 26 gates, 22 restaurants, two dozen retail outlets and up to 20 security lanes. The feel there is hip -- more so because JetBlue has offered T5 concerts by artists including Sarah McLachlan, Daughtry and a capella group Straight No Chaser, not to mention an October concert by Taylor Swift.

From T5, JetBlue offers approximately 150 daily departures to 51 destinations. The number will increase to 52 when JetBlue begins Turks and Caicos service in February, and to 53 when summer Nantucket service is included.

Of note: Delta realizes it needs a better terminal to compete at JFK, and has said it will spend $1.2 billion to expand its antiquated quarters.

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Delta Terminal at Detroit Metro Airport

Northwest opened its $1.2 billion, 122-gate Detroit terminal in 2002, replacing an ancient facility. Passengers on other airlines use a second new terminal that opened in 2008. Following the 2008 merger with Northwest, Detroit became Delta's second largest hub.

Today from Detroit, Delta offers 580 peak-day departures to 147 destinations, including 20 international destinations. Detroit is among the country's principal gateways to Asia, with non-stop flights to Hong Kong, Shanghai, Seoul, Tokyo-Narita and Nagoya. Additionally, Delta recently began service to Sao Paulo, the first non-stop flight between Detroit and South America, and plans to begin Tokyo-Haneda service in February.

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United/Continental Terminal E, Houston's Bush Intercontinental Airport

In Houston, Continental reopened the final phase of 23-gate Terminal E (above), which handles international flights, in 2004. It reopened Terminal C, primarily for domestic flights, in May 2010. The renovations cost $300 million and $65 million, respectively. Houston is the largest hub for the new United, with more than 45,000 passengers boarding each day, or 16.4 million each year.

Like many modern terminals, including T5 at JFK, Houston's Terminal C (not pictured) does not include the traditional row of ticket counters positioned against a single wall, with travelers waiting in line for service. Rather, the terminal includes 115 check-in locations at check-in islands, including both kiosks and counters. Terminal C had not been upgraded since it opened in 1981.

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