The hard thing about giving up a Mac is their excellent touchpad. I tried the XPS one and it's nowhere near.
The 8GB limitation is really unfortunate.
Kind of hard to make recommendations without knowing why you're looking for an alternative. Is it price? Do you prefer to use Windows/Linux and want something with one of those installed out of the box? Don't like Apple keyboards? Don't like glossy screens?
Have you taken a look at the Thinkpad X1 Carbon? I always hear nice things about it.