Also, another reason I am more prone to avoiding the full orchestra these days is because there are not many good sample library options available for writing orchestral music despite market saturation. It's sad, really.
I have a whole bunch of pieces, dating back years, that were meant for orchestra, but I don't know they'll ever see the light of day because I can't afford that many live musicians and the samples struggle too much to play them convincingly.
So I would say that virtual orchestra is most challenging. More challenging than a real one.