We stayed in the Chillout Pera Hostel for 4 days and were very happy with our choice. The hostel is located right at the beginning of the famous Istiklal Street, and we were a bit worried because of the noisy nightlife. The hostel turned out to be very clean and suprisingly quiet. The rooms are big and light, in fact more like a hotel room than a hostel. The shared bathrooms also are well looked after and spacious.
If you want to have a lot of different people arround you and get in contact with other travelers, maybe you should stay in another place, but if you look for an affordable and quiet accommodation, the Chillout Pera is the right choice.