Olarain is listed as hostel, but what you really get is a regular hotel room. Clean, maybe a tad small, but it was all I needed. It is part of a student resident, but it was absolutely quiet when I stayed there. If you need to stay near Antiguo, then you'll have most places within walking distance. I'd probably stay somewhere downtown or in Gros for visiting San Sebastian, although you'll have several bus lines run frequently to get to the center.