On both programming desktops I have two 27" 1920x1080 monitors, one of which in portrait mode.
I've used various over the years, and even very old setups where e.g. windows couldn't be dragged between screens were a substantial improvement in productivity particularly in an environment where a demanding director was inclined to 'phone me at any hour of the day (or night).
I'm currently fortunate enough to have a 30" 2560x1440, some obscure Korean brand (which actually turns out to be a very good performer) which I got for a song /but/ had the expense of driving over to the Stockbroker Belt to collect it from the graphics designer who'd out grown it :-)
If I had to choose, I think that resolution is more important than size particularly if one does not have to jump around, view the screen from the far side of the room and so on. After all, even a relatively small screen can be moved closer, even if it results in (for us oldies) the purchase of a different pair of spectacles. The extreme case would be some sort of head-mounted display, but it's going to be a long time before that sort of thing is really usable for sustained editing etc.
MarkMLl