Here's how to avoid the most dreaded seat on a plane

It's cramped, it's inconvenient, and it's often the only seats available on flights — particularly if you book at the last minute.

In the past, an easy way to ensure you get an aisle or window seat is to book the flight early.

However, airlines have figured out that their customers have an almost universal hatred for the middle seat.

Not only that, airlines have come to realize that many are actually willing to pay to avoid it.

For instance, Delta's cheapest tickets these days fall under its Basic Economy class which only allow passengers to select their seats after checking in — at which point the window and aisle seats are likely to be already gone.

This means passengers will have to buy more expensive main cabin tickets in order to select seats at the time of booking.

On the other hand, Southwest — which doesn't assign seats — charges passengers $15 for the privilege of boarding early.

First, in spite of the revenue generating fees airlines have come up with, booking early is still the best way to ensure you don't end up sandwiched in the middle. In addition to an increased likelihood of getting an aisle or window seats, booking early will also net you cheaper ticket prices.

According to a study by Expedia, the average price of tickets are its lowest 57 days ahead of the flight. Further, the study also showed that those buying tickets more than three weeks in advance on flights within North America can expect to see savings of roughly 43-56%.

In fact, savings from cheaper tickets prices may allow you to "splurge" on the fees for aisle or window seats.

However, there are ways to reduce the likelihood of ending up in the middle seat by taking flights using planes with fewer or no middle seats on board.

Instead of the 737 and A320, look for flights operated by Bombardier C-Series, McDonnell Douglas MD80 series, MD90, and Boeing 717-200 jets. These aircraft feature five-abreast seating in a 3-2 configuration — meaning there is only one middle seat per row.

In the US, the MD and 717 aircraft are mostly operated by Delta, American, and Allegiant. However, many of these aircraft are aging and their operators are working quickly to replace them with planes that are newer and have more seats. American is in the process of replacing its MD80 or Super80 aircraft with new Boeing 737s. At the same time, Delta is beginning to retire older MD88s in favor of new Airbus A321s. With that said, Delta's fleet currently features more than 270 MD88, MD90, and 717 jets. Which means they'll be around well into the next decade.

Another option is to take flights operated for the major airlines by regional carriers under names such as Delta Connection, United Express, and American Eagle. These flights are generally operated using regional jets or turboprop airliners.

Although they are smaller and more cramped, regional aircraft are generally setup in a 2-2 configuration which means there are no middle seats. For this, look for aircraft such as the Bombardier CRJ, the Q400 turboprop as well as the Embraer ERJ.

Unfortunately for many flyers around the world, the narrow-body airliner fleet in Asia and Europe is a virtual duopoly split between the 737 and the A320-family. As a result, apart from encountering the odd C-Series, E-Jet or 717, passengers will have to fly on a regional jet to avoid six-abreast seating.

These large jets are generally setup with nine or even 10-abreast seating in a 3-3-3 or 3-4-3 configuration with either three or four middle seats per row in coach.

For flyers looking to avoid middle seats on long haul flights, there are several types of aircraft they should hone in on.

First, Boeing's venerable twin-engine 767 wide-body is still around and can commonly be found with a 2-3-2 configuration. That means there's only one middle seat per row in coach. It should be noted, however, that many of the 767s are pushing 20 years of age and like the MD80/90, airlines are in the process of replacing them with newer models.

Fortunately, for flyers, the A330 one of the most popular wide-body airliners in the world with about 1,500 examples in operation and is still rolling off Airbus production lines. In fact, the company is currently selling a next generation version called the A330neo.