Usually I think of laptops being aimed for a buisness in which you travel sometimes. So the "light" one would be better for that. But if you really want one to just have or show off get the "heavy" one that is probably not going to move much but is able to.
As far as what you want I would look at these first.
Weight- you dont want to carry around 10lb. You want light for buisness but I wouldn't care if its just for showing off.
Size- look at screen size,width of laptop,etc...They are portable, but they can be a hassle to carry.
Type of screen- I dont usually dont care about this but you might. TFT and XGA are two types.
Basic computer stuff- This includes hard drive, ram, stuff like that. I wouldn't expect to get much since its a laptop and they cant fit it all in there. You're probably going to get a Centrino and I would recommend it.
Battery life- Again, for business- lots of time. No use- Probably going to be hooked up directly.
All of this is decided on why you want it, where you will use it, and how you will use it. If you are getting one just to show off, dont. Laptops are costly and desktops are much better.