I agree with Avon Lady. Comfort is really the only difference between planes. Comfort taking into consideration maximum cruise speed, as well as leg room.
What I'd like to see is a plane with fold-up cots on them. Just really simple fabric cots (maybe with some memory-foam for cushion), and have them stacked to the top of the cabin. Say 4 high in "economy", 3 high in business, and 2 in first class. For crash protection, you'd have to have a fold-down brace that slips around the body and you put your arms through it. Mothers carrying babies would, and other "handicap" people, obviously, have to have a different sort of arangement; I'm talking about the bulk of fully capable adults. You'd have to climb a ladder to get to the top rack, so only "skinny" people (
) could/would go there, and maybe get a significant discount.
You could fit more passengers. Long hauls would be more comfortable. People are more likely to sleep. Small LCD tv's could be integrated into the upper cot even easier than the seat backs. I imagine crash safety would also be improved, since current seat belts rely on holding your pelvis to the dismay of your spine; the lie-down design would use your legs, upper torso and arms.
Airbus and Boeing both suck. They need to develop a lie-down plane design.