I've spent four nights at Gardiners, in a 18 persons mixed dorm, chapel experience. The room was amazing, kitchen and bathrooms were clean and nice. About 10 minutes of walking to be at the center of Dublin.
The only 'problem' were my roommates, who snore very loudly (but I was expecting that and brought some earplugs) and once some boys even brought two girls over night who shared their beds! I know that they weren't guests of the hostel as they sneaked out in the early morning. That was a total no-no and also not allowed! I would have expected the reception to be more careful about that, as at night you have to show your key-card to enter the hostel.