I dont know what the "ideal size" is when the programmers and designers took there choices.
But I do know it felt a little small on my 22"-monitor. Now I have 24" and this rocks hard. I should say 24" is the best choice you can do, if you have the room for it.
Everything is clear and nice sized. I have not felt I miss anything since I changed. Before I could feel that some things were to small.
To have bigger than 24" would be too big and will fill no demand.