Here are the hostels I’m staying in this summer, obviously I can’t recommend them personally but they were all pretty highly rated and seem to offer a lot, I’m excited about them:

Paris: Vintage Hostel
Florence: Florence PLUS
Madrid: Way Hostel
Barcelona: Equity Point Sea (also have Equity Point Centro thats a bit more expensive cause it’s in the center of Barcelona)

for Rome I have heard a lot of people like Alessandro Downtown (we instead chose a budget hotel in a much, much better location- I don’t like the area around Termini Station).

Anyways the best way to search hostels is to use eurotrip’s hostel option, plug in your dates and then search through the options. See what the hostel offers (sometimes it’s worth spending a few extra euro in more things are included, like breakfast and wifi; also will tell you about location, if the hostel has a bar and kitchen, etc.). READ THE REVIEWS!! I really relied on what lots of people said about the hostel to make my choices. You can also book using eurotrip.
Hostelworld is another good site to use for research and reviews.

Never stayed in a hostel yet, but i can tell you where i’ll be staying when we leave mid june too!
Ams – Stayokay Stadstoelen – great location outside of the crazy red light district so hopefully we can get some sleep after coming back from it. Seemed to be cleaner and cheaper than most right in the best nightlife areas.

Barcelona – Hostel Kabul – top 10 party hostel in Europe. Great location. Nuff said.

Florence – Budget was important for us, so we wanted to spend less on hostels in certain places, and Florence we decided to spend less, found a great little hotel which gave us a 4 person for like 16E a night – Casa Dolce Casa.

Thank you both so SO much for your help! Will definitely take on your advice & read the reviews!

DreamingOfItaly, what’s the name of the place you chose to stay at in Rome?

Lysh X

Hotel Arena-House. Located right near the Colosseum. I’m traveling with 2 friends, so a triple for us was very cost effective, as Rome is fairly expensive for hostels/hotels. We’re playing 30 euro each a night.
Google for their website; I booked direct through their online booking.

Bruges – I stayed for one night at the St Christophers there and hated it. They were doing renos and my room happened to be over the bar area so there was little sleep to be had since they kept the music going late. I moved to Snuffel for the rest of the time and loved it. Nice small bar, more laid back, better location. And cheaper.

Amsterdam – I stayed at both Flying Pig hostels (downtown and uptown). They were both excellent and I heard interesting things about the cleanliness of other hostels. From what I heard from the people I met, stay away from anything in the red light district. The downtown was closer to the city centre, just a couple minutes from the red light district, bigger and more partying. The uptown was smaller, more laid back but was still close to it’s own nightlife district and was cheaper. I went on an awesome pubcrawl in the area.

Cologne – I stayed at Weltempfänger Hostel, which was very clean and nice hostel, but not really a party destination. I had cool people in my room, but it was otherwise harder to meet people there. They had a kitchen and a cafe downstairs. I didn’t go out much in Cologne, so not sure if it’s close to nightlife.

Paris – Stayed at St Christophers. It was a huge hostel! They had a restaurant which served sub par food, but the club downstairs was pretty cool and there was lots of locals that came to party. It’s kind of far away from a lot of things, but the subway system is easy to use. It was clean, but I didn’t think it was anything special.

Hope that helps a little!