i used the dell 1920x1080 and it's fine if a little small. interestingly it comes standard with the dpi setting set to increase font size to make it easier to read.
it's strange though, i use a 14" laptop at work with 1400x1050 and i find it's absolutely fine. but i can't run that resolution on my 19" crt at home. just seems a bit small...
another thing to bear in mind when doing the price comparisons is the software you get with the mac - definitely a better set of apps than the dell