If seat width/pitch and all other things like lavatory/passenger ratio as well as the size of the lavatory are the same, why would I care? Likely the lavatory and window seats will have a bit less simply curvature of the design, I'm sure they round down on everything not up on other things so it will be worse, but for the convenience of more frequent flights or new direct to direct w/o a connect I'd take that if I get that advantage

Personally, I feel that 2 aisles makes a huge difference in the feeling of space and enjoyment of the flight. A single aisle flight would be claustrophobic for me on an extended length flight. I especially like the 767's 2-3-2 layout for long flights in coach.

FWIW, the A321XLR, which its the impetus for this conversation, publishes a 4700 nautical miles (~5400 statute miles) but most airlines expect it to fly less than that owing to winds and such. So 10+ hour flights aren't really going to be the way it goes, but 8+ certainly will.

And passengers will line up when they get non-stop flights bypassing hubs or cheaper fares as a result. We've seen that over and over again throughout the industry and time.

There are two main drawbacks the A321XLR has relative to modern twin-aisle aircraft: environmental factors and lav space. Cabin pressure will be lower (~8000 feet rather than ~6000 feet on newer composite frames) as will humidity. Both of these impact the onset of jetlag for travelers. Twin-aisle aircraft are required by law (in many/most jurisdictions) to have an accessible lav on board; single-aisle are not because when the rules were written they didn't fly that far. With that changing it will be interesting to see if the rules follow.

And then there are the myriad configuration choices that the airlines make when configuring the aircraft. For example, the brand new AirAsiaX A330neo is not going to be a particularly comfortable ride for long-haul flights in the back, even with two aisles. I sat in the seats (I'm on the left). The 3-3-3 layout is not nice.

Anything longer than a NA transcon for me and I will always choose a widebody and sit in J.
Anything NA transcon or shorter, I'm fine with a narrowbody in any cabin.

I'll avoid narrow bodies on medium haul travel unless the economics really make sense.

I'm going to admit it: as much as I like talking about which types I like and don't like, it almost never affects which flight I actually book. If it's 10 hours, there's a good chance I'm looking for award space in J and accepting whatever aircraft type I get.

If I'm buying a coach ticket, then I'm more concerned about the seat dimensions and my probability of at least finding myself into an extra-legroom seat or, better yet, a true premium economy seat.

The only time I actually look closely at the aircraft type is when I'm buying paid J for long-haul work trips. Then, because the fares are often the same for a bunch of flight combinations in our corporate booking engine, I'll drill into the routing and types. In most cases, it's MCI-XXX-DXB-Destination, so I do look for the A380 on the XXX-DXB part. This route obviously has no narrowbodies (the other choice is a 777), but if I flew a route with a choice I'd probably opt for the bigger plane, assuming the J seats were considered roughly equal.

That's a good point, but for the level of cabin (dis)comfort I can imagine here, it better be door to door service and come pick me up from my house...:D

I usually doze off right after take off (I rarely miss!) so I usually don't mind being in a narrow plane. My claustrophobic wife would of course have a different take. And where she'll be--that's where you'll find me too. LOL

After a six-hour flight from Massachusetts to Florida in a paratroop-rigged C-47 (military version of DC-3), "seats" were rows of webbing along the sides, and nothing blocking the open door but a few strips of webbing whose strength nobody wanted to test, I'll take a jet with real seats, pressurization, lavatories, food/beverage service and 500-mph ground speed any day. The seat matters to me. The food/beverage service matters to me. How many aisles? Meh.

My first trip to Hawaii was in a C-130 sitting on the webbed seats. :) 8 hours from an airfield near Sacramento to HNL. Fortunately that's a pretty roomy ride for 50-60 people, and we had coolers full of sandwiches and drinks.

yep, been there: Aug 1977, Van Nuys to HNL, droning along at 23000 ft or so for 8+45 in a Lockheed Converter ("It converts Jet A into noise, smoke, and vibration") just like the one you mention

Ahh..but every seat had aisle access!!!!

I agree. To me, the only difference between a widebody and a single-aisle is that there are more of my preferred seat (aisles). Otherwise, I don't see any positives/negatives in either type of plane (assuming they both have the same seats in terms of width and pitch).

A six-across economy seat on a 707 in the 1970's or earlier would mean excellent in-flight service and plenty of legroom. I would happily take that over a widebody with cramped legroom, nickel-and-diming, and a decent chance of rude staff.

Just flew BOS->LIS on Delta narrowbody and that's about a 6.5hr flight. It was rather uncomfortable for many of the reasons you mentioned above, especially with a 3 month old and 2 year old in tow. The bathroom situation was really not good. On a 6+ hour flight many more people will use the bathroom many more times than on, say, a 3 hour flight where some might avoid using the bathroom at all. The lines were constantly long and the bathroom immediately filthy.

(The other reasons the flight was uncomfortable had more to do with the DL cabin crew than the plane itself...they rarely came through the cabin to collect trash or service items, they did not offer water or beverage service except at meal time and when I went to the back to ask for some water (I was breastfeeding and therefore extra thirsty) I was given the stink eye)

In the future I would consider other routing options from the US to Europe that involve a wide body