Where in Lisbon should I stay in September?

[ChinchillalatlClever]

I visit Lisbon with a friend from 16th - 21st of September. Whenever I spend some time in big cities, I try to find a place to stay close to a good area for bars, students, shops etc. We're students ourselves, so is there a part of town that you can recommend? Do you even know the name of a hostel?

Thanks!