Hi rainbow,
I seem to have crept up to 19" with the two I had narrowed it down too, I should just a say get away with 19" on my desk (just won't be able to get at the window at all).
I'm leaning more towards the 19" Samsung as it appears to be hight adjustable, pivots and swivels - the rest of the spec seems very similar to the 19" Viewsonic.