I personally *haven't* seen the BenQ or the Dell in person I have however seen a friends 'EIZO Flex Scan S2411W' it looked excellent, deep black blacks, amazing colour, no backlight bleeding, etc.
He's a professional graphic designer and says that's the only monitor he has ever used that has come close/surpassed a good quality CRT in colour reproduction.
I don't know what you're going to be using it for but if you want colour accuracy going by what he has said I'd go for the EIZO especially at £450, he paid over £1,000 new.