Like most writers, I'm rather attached to my computer. I currently use a Dell Inspiron with a 17" screen and love it.
The most important aspects of the computer are the screen size followed distantly by battery life. You may have noticed that this screen size, in the era of tablets, is becoming increasingly difficult to find. The width and overall size of the screen allows me to open two Word files simultaneously, which is particularly helpful when translating editing or proofreading notes into the master draft of one of my books. And when I'm writing a first draft, the large screen allows me to have the draft and my design documents open at the same time.
But there is one thing about the giant laptop I don't like -- it's lack of portability. The computer is a beast. It was difficult to find a backpack that could contain it, and when I carry the machine around in the pack it feels like there is a boat anchor back there.
The monstrous size of the screen also seems to be directly related to the shorter (although, not terrible) battery life.
I've experimented with smaller laptops. We have a tiny and much older Dell Inspiron Mini 10 which I've taken on a few vacations. It is less than half the size of the "luggable," but it seems to offer less than half the utility. Still, it isn't a bad compromise when you have to carry it around for hours, rather than perching it semi-permanently on a desk, table, or kitchen counter (where I actually do most of my writing.)
So I guess I'll stick with my giant laptop, even if that makes me look (even more) like a dinosaur!