2.5" are generally built a bit more shock resistant, since they are generally intended as laptop HD's, so you would have that going for you
As you said, less heat, and less power is always better as well.
Try and figure out what you are putting on the drive to determine of 80 gB is enough for you or not. My laptop drive is 100 gB, and I have 20 gB of mp3's on there, 4 games, including Civ 4, and probably about 10 gB of other personnel data, and I still have about 40gB free. You may be different. I know I don't have any movies on my laptop, and those can take up a good bit of room. It all depends on what you plan on putting on there.