By now, most travellers have heard about the new Airbus A380, the giant double-decker that is known as the largest commercial passenger aircraft in the world. But what a lot of travellers may not know is it’s not the longest one. That honour currently goes to its relatively slender sister, the A340-600.

Unless you are an aviation geek or super-frequent traveller, you probably don't know, or maybe don't even care, what type of aircraft you'll be flying on, as long as the price is right. But choosing the best aeroplane for a trip can make a big difference in terms of personal comfort.

Renovations and last minute aircraft swaps make choosing the best aircraft an inexact science, but aeroplane size and age are the most critical factors. Some tips for making the right choice:

Bigger is almost always better.
For long-haul flights, your first choice should always be a jumbo or "wide-ride" jet with two aisles. These big birds include the Boeing 747, 777 and 767 or the Airbus A380, A340 or A330. The sense of space, overhead bin room and access to lavatories are much better on jumbo planes. Two aisles make it easier for flight attendants to serve passengers and there's more room to get up and walk around during long flights.

Bigger has its downside.
Moving more than 400 passengers on and off the plane can take a long time, especially if you are seated at the back of an A340-600 - the longest passenger aircraft in the world. While two aisles make it easier for flight attendants to serve passengers, it can take longer to make it down the length of the plane. Waits at customs and immigration are longer because of the greater influx of passengers all at once. Also, many older 747's do not have seatback entertainment systems, and getting a good view of the overhead screens might be a challenge.

Beware transcontinental or transoceanic narrow bodies.
In the US, nearly all transcontinental flights were once wide-bodies such as the 767 or even 747; these days, the opposite is true, with smaller 737s, 757s and A320s plying the cross-country route. Airlines that did not want to abandon lower-volume routes keep them by deploying smaller aircraft. The trend toward smaller jets is quietly occurring over the Atlantic, too, as new advances now allow airlines to fly over the ocean with two engines instead of three or four, which makes flying smaller aircraft on the routes more feasible.

Several airlines now fly single-aisle 757s on "thin" transatlantic routes. For example, Delta Air Lines uses 757s between New York-Kennedy and several (mostly smaller) European cities. Continental does the same out of its big Newark hub. US Airways uses a 757 between Charlotte and Dublin. Smaller planes mean only one aisle, fewer aisle seats, less room to walk around in and less access to lavatories, which can make a difference on long-haul flights.  If you like your jets big, be sure to check on this before you buy. If a third party aggregator does not include the aircraft type, it can be found on the airline's site.

Newer is almost always better.
To book a newer aircraft, refer to the numbers that come after the hyphen in the model number. For example, you'll get a much nicer ride on a 737-800 or -900 than an ancient 737-400. The current newest version of the Boeing 747 is the 747-400. But next year the brand new 747-8 Intercontinental will enter commercial service offering up more space, better in-seat entertainment, new cabin lighting and bigger, brighter lavatories. In the US, younger low-cost airlines such as AirTran, JetBlue and Virgin America have the newest fleets. Worldwide, Asian and Middle Eastern carriers have the youngest fleets.

So next time you are booking a flight, use this quick reference guide to help choose your aircraft based on size:

Extra-large: Airbus A380; Boeing 747 (both have two aisles and two levels with capacity of more than 400 passengers)

Large: Airbus A340, A330, A300; Boeing 777, 767, MD-11 (All have two aisles with capacity in the 250 to 400 passenger range)

Medium: Airbus A318-321; Boeing 757, 737, 727, 717, MD80-90, DC-9 (All single aisles with capacity of around 150 to 250 passengers.)

Small: Embraer ERJ135-145 and 175-190; Canadair CRJ100-1000. (All single aisle "regional" jets with capacity of 50 to 150 passengers. Warning: these "Barbie jets" are frequently used on decidedly non-regional routes. Avoid them if you can for flights longer than 2.5 hours.)

Do you have a favorite type of aircraft? Which one and why? Leave a comment on our Facebook page.

Chris McGinnis is the business travel columnist for BBC Travel.

Correction: An earlier version of this article mistated that the size of a jet also affects safety. This has been changed.