Have to say, if it was me I would go for the skyline. I have stayed there 3 times this year as a gold, and got upgraded every stay. I must have a nice face or something.

I have to say I prefer the Hilton, and have stayed there 3 times this year. Its newer, and very convienient for T4 as I fly BA. I also like the Zen restaurant inside the hilton, which is very reasonably priced.