I travel a lot. Not as much as flightcrews...but int'l several times a months in different classes.
Here are some impressions:
The A320 is quieter than the 737NG's (sorry boeing). MD80's are quieter than both....
The extra width in the 320 cabin is not noticeable in the seat or the aisle (sorry airbus).
The 340 is also quieter than the 777....however it's cabin is considerably narrower..and appears claustrophobic after eight hours.
Actually for economy travel, the 767 is nice..even though narrower still than the 340.
The 777 sounds/feels/rides like a more 'substantial' aircraft. However....it has a 'fishtail' motion in the back that is annoying. I noticed this trait on the 744 as well.
All seats in business class are nice....even in the middle seat. It's just not the same as in economy. Seven across is fine.
British Airways is ok in economy, great in Club World. SQ anc CX have great products too...but not really any better. Qantas in first class is a real treat (and real rare for me...)
You can tell the difference in AA's new coach configurations--it makes a narrowbody tolerable for longer flights.
Continental does try harder...but not all the time. I've been treated just as well by AA, TW, and UA.
I don't care for Northwest and I avoid them.