Definitely a PC or Linux Box (Maybe go with Windows and Install Linux on the side). Something with a good amount of processing power and plenty of RAM. If you do any CUDA work or pentesting you may want to invest in a good nVidia GPU as well. Go with something with a i5 and at least 4GB of RAM. A GeForce 310 or equivalent should be plenty to test out CUDA applications. As far as branding is concerned: HP, ASUS, and (high end) Sony are good buys. Avoid the following: Dell, Gateway, Toshiba, Samsung. Again, this is just my opinion and some people may argue with me but I used to work in University IT and have seen countless laptops fail. The best and most reliable boxes that I've listed come from experience in the field, along with the worst.
Whatever you do, do not get suckered into a Mac. You will wind up having to buy a copy of Windows because your applications will not be compatible. I do not say this because I do not like Mac, I say this because I both was an engineering student myself AND worked at an IT help desk for my university, watching all sorts of kids who bought Macs bring them back because they can't use them in school. I love Mac, but they are not for engineers.