For me if its one big screen (with extra resolution, no point otherwise)
OR
2 screens, say 19" side to side, the classic “crack down the middle approach”
I’d go for one big screen every time, you can see everything, and your plug ins take up less screen space
But I have a 27" High res in front - for arrange page/workspaces - can even bring up the mixer on top and still see what you are doing easily
And a 19" at the side with metering (Voxengo Span) - control room mixer, and any mastering plugs open 
Big screens do cost a lot but ‘no gap in the middle’ … But check your graphics card can support one or youll need to factor in the cost of a new card too