It's really personal preference with laptops. Depends on the application. Some of my clients want smaller, lighter laptops for traveling, some want larger, with larger screens for usabity. I always encourage my customers to go to a store, touch & feel before making a final decision. I also warn them about things like battery life, upgradability, etc with a laptop. I consider laptops to be disposable, average life span 2-3 years.
My brand recommendations to my clients in order of ease to work on (from a service point of view, and I make it clear that's the point of view I'm giving them):
sony
toshiba
dell
Scott
Edit: I personally use a sony pcg-tr3 - getting a little old, but small, sweet... might pull it out of my trunk once a month.