Note that in Spain and in parts of Latin/Hispanic America, "hostel" has a different meaning that what we often think of in the U.S. and other places. They are akin to pensiones in Italy. Private rooms and possibly even private baths. I stayed in several nice ones in Andalucia.

As for the HI type of hostel, I have stayed in a few (both actual HI hostels and others of the same format) with mixed results. I did not like the Seattle HI. While there was secure bike parking in the basement, it was like sleeping in a multi-bed dorm room. I think both times I stayed there my room had at least 5 bunk beds. Young people coming in late after partying and people snoring all night makes for a poor sleeping environment. At the other end of the spectrum was the relatively small HI hostel at Lake Itasca, MN. The Bar Harbor, ME hostel closed during the day, so you had to be out until it re-opened around 5:30 p.m. or so. Staff can also affect the experience. The woman running the Breckenridge, CO hostel where I stayed was generally unfriendly, as if she hated her job. I and a couple had to leave very early one morning. The woman seemed to enjoy telling us that she would not be available to give us our $5 key deposits back until at least 8 a.m. the next morning and refused to give us our $ the night before on faith that we would not make off with the keys. So we left with the keys at let her keep the $10.