Even without considering the relative merits of the monitors, are you sure you want a 21" screen?
This is only a personal thing but I find a screen that big is too much as a lot of info towards the edges of the screen appears in your peripheral field of vision and doesn't have detail unless you turn your eyes or head quite a lot to accommodate it.
If you're doing CAD or any other design work, the whole of the screen is important and I find that anything over 17" diagonal quite uncomfortable after an hour or so, even taking the recommended breaks in work pattern.
If you're used to a screen that size, fine. If not try and get to use one for an extended period before you commit yourself.