Though I’d just comment on the trip as a whole:

Madrid: Way Hostel- very good hostel. Clean, cheap, and great location. Staff is very nice and helpful. Has a lounge area and kitchen were people hang out, and the hostel organizes pub crawls at night. Quiet at night. Definitely recommend this place. Only negative: no air conditioning in the rooms, fans don’t do much to cool you down.

Nice: Villa Saint Exupery. Probably a little more on the expensive side, but worth every penny- this hostel is amazing. The staff was the best staff I encountered on my trip- really knowledgeable and had tons of suggestions of what to do. Clean, has breakfast included, tons of free computers to use, huge lounge and bar area that serves cheap drinks. Kitchen prepares cheap meals, or you can use it to cook your own. Tons of other little stuff included as well. It can get loud at night (esp. if your room is downstairs) but I never had a problem sleeping.

Florence: PLUS Florence. Good hostel. It’s HUGE, with tons of options for dorms and private rooms. Runs a lot of tours and pub crawls and organizes reservations for museums, which is very convenient. Rooftop bar was very nice. There’s lots of good hostels in Florence, but this place was fine.

Athens: AthenStyle. This hostel was excellent- great staff, very cheap, and the rooms were big and clean. Rooftop bar was awesome and had a great happy hour. It’s not in the greatest of areas but still I felt perfectly safe and it was in close walking distance to all the major sites.

Santorini: Villa Manos. This wasn’t a hostel, but more of a B&B type place, and we loved it. Beautiful little place, with an open patio and pool with tanning beds. Staff was so nice in arranging anything we wanted (picking up at the port when we arrived and driving us to the airport on the last day, for example, at no additional cost). We also got a free room upgrade, which was a nice surprise. Nice, basic, clean rooms and bathrooms at a cheap price. Decent location- 15 minute walk to Fira, or a bus stop right across the street. (We rented ATVs for most of our stay to get around the island). Highly recommend this place.