First off, I'll give you some backround information just because I think it's rellavent in this situation.. just don't mind my spelling and grammer cuz I know its garbage.
I have built my own computers since the 486 was the best you could buy... I sold PC's for almost 4 years and worked in home theater sales for almost 7 years... I have descent knowledge of upper end LCD and Plasma's like Sony XBR5's and Pioneer Elites and work with them all day long.
That being said, what i'm offering you is nothing more than a personal opinion.
There is no right or wrong when it comes to buying an LCD monitor.. There are pro's and con's to TN panels... simple as that. They are not crap like some people will say.
Can they reproduce colour as well as SPV-A or MVA panel? No... Is their viewing angle as good? No.
BUT
They are cheap compared to other options and are great if your looking for a fast responce gaming monitor for a good price. If your eye is not trained well, or you do not have two monitors side by side to compare a lot of people cannot tell the difference between an upper end LCD monitor and a cheap one.
Go look at something like a Samsung 225BW or 226BW.. There's tonnes of people online who will tell you that they are amazing gaming monitors even though they are TN panels.
As for 20 vs 22... they are both the same resolution and the same aspect ratio so neither will look streched or compressed. One is just bigger than the other.. Also, don't go by all the numbers the manufacturers give you.. most of them are total BS... If you can, go look at some monitors and buy the one that looks the best to YOU that you can afford.
If you want a suggestion, look for a good deal on a Samsung 225BW or 226BW.. for the price they are a great gaming monitor. Are there better monitors out there? Sure.. but unless your playing on something like a 34 inch widescreen XBR CRT or a 60 inch Pioneer Elite plasma there will always be something bigger or better.. its just a matter of budget and priorities.
Here's some info for you:
http://www.pchardwarehelp.com/guides/lcd-panel-types.php
Hope I could help.