If you are changing from square to widescreen, then I would go for a new monitor which has at least the same height as the old one. That way, you will just appreciate the extra width; without any loss of height.
So, I was thinking if it has to be a wide screen may be a 22" ?
Line One:- Zen - DrayTek Vigor 2600VG
Line Two:- EntaNet (Aquiss) - DrayTek Vigor 2600