I'd go for Abraham House. Its 11 Euros in the cheapest dorm, plus is very close to the main street, O'Connell Street, and the central bus station (great if you are coming/going to the airport as I always am when I visit Dublin). I stayed there for one night and I found nothing too objectionable. They need to redo the bathrooms but they weren't very terrible. Offers a pretty decent breakfast. Staff was friendly and helpful when I arrived at 2 AM and some troublemaking dormmates decided to steal the pillow from my bed!