What's the best external hard drive for gameing?

I’m going to be working in a computer lab, just making sure nothing is stolen. While I’m there, I plan to bring an external hard drive with PC games on it to play on the lab’s machines. I’d like to know if there is a particular brand or model that would be best (and cost efficient) for playing games. If it helps, the games would be mostly steam titles and a few old RTS’s like “Tzar” and “Warcraft 3.” Capacity could be anything over 320GB.