Compared to the LG, the GW2765HT has a frame of input lag, a perceived black depth ruining glossy black bezel, worse colour presets, no hardware calibration and slower pixel response times. The Dell U2515H has slightly worse colour presets and has an inner black bezel which ruins the perceived black depth since it is not actually frame-less. Example: https://www.flickr.com/photos/97364704@N08/15631381856/
As a result, BenQ is a bad deal, no need to talk it further. Given the price of the Dell, the Dell is a good deal, but it has the shortcomings I mentioned above and 25" is a bit small for 1440p.
My opinion is that because you buy a monitor aiming to keep it a full decade, buy the best you can afford. In this case, the LG it is.
If it is the shop that you cannot / do not want to deal with, the next best choice is this Asus:
http://www.amazon.co.uk/gp/offer-listing/B00LGE29SK?SubscriptionId=AKIAIXNYVO2SJEYIT5VA&tag=geizhals-am-21&linkCode=xm2&camp=2025&creative=12734&creativeASIN=B00LGE29SK
It is also flicker-free, has excellent input lag and response times, but has slightly worse color presets than the LG that cannot be fixed through OSD.