Firstly, right category.
I would opt for the ASUS MX279H, as it is a really nice Asus monitor with AH-IPS screen, All for a pretty good price. The Dell is good, though you may find it is quite expensive. Doing work, I find the larger 27" monitor best.
But; If you like gaming, I would strongly suggest the ASUS VG248QE, it is 144Hz, compared to the others 60Hz, that is more then double the fps viewing speed and the sharpness and crisp is much better then any other monitor listed in terms of gaming use.