I own an Eizo S2410W, the older version of the monitor you are thinking of buying. I also used to own a Dell 24" - I can't emphasise enough, the difference in quality between the two if I painted it in large, red letters on the side of your house, which is even more surprising as they both use the same panel. Just goes to show the electronics driving the panel are as important as the panel itself. Really, they are worlds apart.
I can't comment on the BenQ as I have never seen one.
If you have the money, you really can't buy a better monitor than Eizo until you get up into the £2-£3K range and the likes of some of NEC's SpectraView range.