My daily driver is one of the Casio Pro Trek series of watches, for exactly the reason you’re looking for. It has a “world time” mode where you can display the time in any time zone (including GMT of course) and (quite usefully) your home time is permanently shown at the bottom of the display.
Of all the watches I have, it’s simply the easiest to use while flying when I need to switch time zones. I almost never set it to display UTC though, for the simple fact that the airplane clock will only display UTC, so I don’t have much need to display it on my watch.