Which budget gaming laptop should I buy...

So I have actually never had a laptop before but I'm not an idiot when it comes to what makes a good one. I've been researching for a week or so for a good budget gaming laptop I can get (for about €1000).

I live in Ireland so laptops here aren't as cheap and it's much harder to buy MSI laptops and Razorblade laptops here.

I've narrowed my choice down to three choices:
Asus ROG GL552 - €1150
Dell inspiron 7559 - €999
Dell XPS 15 9550 - €1450

Note : I would be using the laptop for some gaming, watching videos, some editing work and everything in between.

I know the XPS 15 isn't a gaming laptop but I love the overall fit and finish and it does have an NVidia GTX 960m.

Also I am just wondering which of these laptops would perform the best while gaming and does the ddr3 ram in the dell inspiron effect much of anything (the two others have ddr4)

Dell has 4gb gddr5 (how does this differ from the 2gb in the two others)

Lastly the dell Inspiron has a 4k option which I'm not sure if I should get, the extra €250 isn't an issue and I would love the picture quality but is this what you want if you're gaming?