In general, the more performance you add to a laptop, the less mobile it becomes. If your son is 16 and you plan on getting him the "top-end" type of gaming laptop, he has to understand you can't treat it like a truly mobile laptop, and you have to be very careful with it.
That being said, there are some brands which make slightly more portable iterations of the same basic design, but performance is always sacrificed in the process. So if it's the case that he needs a certain amount of portability, a brand like Dell might be a good choice. The main disadvantage to Dell on a high-end laptop is the price.
If your son can live with a desktop replacement that's not so portable, I still wouldn't go Alienware. The price premium you pay for them is mostly for the name and the aesthetic improvements on the computer (paint, logos, etc...) and generally speaking you don't get better hardware. For a desktop replacement, I'd take a look at brands like Sager (go to www.pctorque.com
) and Hypersonic (www.hypersonic-pc.com