Depends on what you want to do.
Having two 22" LCD will give you a lot more desktop space than a 24" LCD.
If you want to watch HD video at 1080i/p which translates to 1920 x 1080, then you will need a 24" LCD since a 22" LCD only has a resolution of 1680 x 1050.
Also, if you need good color accuracy then you will need an 8-bit panel. 22" LCD uses the less accurate 6-bit TN panels. With the exception of two 24" LCD monitors, all 24" LCD monitors use 8-bit panels. The exceptions are from ACER and SAMSUNG LCDs which are selling for less than $550.
See my responses in the link below where I talk about LCD panel technology. I think my comments will answer many of your questions.http://www.tomshardware.com/forum/243682-28-best-video