In my case, I have a size constraint such that I'm not sure that I can even go with a 27" monitor. Might go with another 24". I'm currently using a 27" in place of the dead one, and it seems okay, but barely so. The desk is the limitation. It's not a great desk, as far as material quality is concerned. It's one of those that would dissolve if it encountered water. However, I'm using every inch of surface on it, and I couldn't easily replace it with a wider one due to space limitations in the room.
Mount it on the wall. Go crazy, get as big as you want.