NCIX.com - Canada's Premier Computer Store - Great Technology, Service and Selection.
Pick out the cheapest one. If your eyesight isn't very good, then you shouldn't go for one with higher pixel density.
NCIX.com - Buy BenQ EW2420 24IN Widescreen LCD Monitor VA LED 1920X1080 8MS DVI 2XHDMI 2X1.5W Spk - BenQ - EW2420 - in Canada
this is a pretty good one for the money, but if you REALLY want to squeeze the pennies, go for the Acers
If you're eyesight isn't that good, then wouldn't it be harder with higher pixel density? (i.e. 21.5" vs 24" 1080p) as the resolution is in a much smaller space, making things harder to read because they are smaller.