The key for most a/c is keeping the seats occupied though that won't help you much on older a/c such as DC9s, 727s, DC-10s and L-1011s (as well as other older a/c).
Originally Posted by
LarryJ
The 757/A320 size seems to be a sweat spot.
757 is good when it's used for ranges beyond 1,800-2,500 miles (but under a trans-Atlantic?) as it can carry more pax/cargo and fuel for these flights and overcome its weight penalty for shorter flights (where the lighter but shorter-legged A321 is better).
The 320s seems to be optimized for flights less than 2,000 miles which is why they have trouble with transcontinentals in the U.S. (ask B6). 321s and 3192 have just that extra range to fly U.S. transcontinentals.
I don't know how well the newer technology in the A380 does at overcoming it's very large size.
Reportedly the A380 at 80% pax does as well as a fully loaded 744.