I'm going to be entering my first year in college this fall, and I've been recommened to buy an external hard drive for backup reasons. I'm only going to be using the external with time machine on my macbook which has an internal hd of 250gb. What size/brand hard drive would you guys recommend? I'm most interested in the 2.5" for the portability, but I'm not sure if HD speed makes that big of a difference. I would also prefer firewire since I heard it is alot faster than USB 2.0. Any suggestions would be great!