I'm fine going transcon say LA-NYC, or NYC-FLL in a narrow body. But I wouldn't want to go transatlantic in a narrow body, and yes that includes a 757 too. Since the 767 isn't considered a widebody now. I'd prefer to go transatlantic in a 767, 787 or 777, or 330.
Why? More room. A narrow body would just seem, too tight for that long of a flight. After about 4-5 hrs. doing my annual transcon from ATL-PHX/PHX-ATL, when I was in college visiting home for the holidays on a DL 757, I was ready to climb out of my skin.
In the 90's the typical equipment for that route was a 757. Occasionally they'd put 767 on that route, it was nice and more spacious. Then America West started doing the route as well and my parents put me on that instead (it was cheaper than DL) and it was an A320. The 767 was still preferred for me. So to answer your question, preference and comfort.