The Dell looks like it is 3 or 4 years old so I would not even consider that.
Both the Asus and Lenovo have Celeron CPUs (same model in both laptops) which are at the lower end, but at your price you would expect that.
Both have the same memory.
Both have 15.6 inch screens.
Both have a DVD drive.
The ASUS comes with a 1Tb hard drive, the Lenovo only 500Gb.
There is not much in it, however the Lenovo seems to be on offer at £199 from John Lewis so as you can trust them I would go for the Lenovo G50.