You can't compare monitors just by specs, in my opinion any monitor with 8ms response time or less is good enough, also don't get contrast confused with dynamic contrast. You can also hardly say that one brand is so much better than the other when you're talking A-brands, because all of the listed monitors have a TN panel and so they all have the same limitations.
In my opinion 20" screens are a big leap forward due to the increase in resolution... from 17" to 19" there is no increase in resolution. In my opinion you'll get value for money if you buy a screen like that 20.1" Sceptre, especially with the $30 mail-in rebate making it $199.