Nice list! I've stayed at some interesting hostels before. The 'Plus hostel' in Florence was amazing. They had a pool, sauna and gym. The cocktails were amazing and there were live performances on the terrace. The beds were really awesome and the room was super clean.

Yellow nest hostel in Barcelona was my favourite. That was the most fun I ever had. They offered free dinner on the rooftop. Everyone just sat together for dinner. That was a nice bonding experience. You got to know everyone and you just end up going out after that. The pub crawls were amazing too.