Hey there, I've never been to Prague but just looked really quick at the websites and they all sound good. You probably can't go wrong with any of the three; they seem similar if not the same in terms of ammenities and price, so maybe go on location? And if you're an easy going person, ending up at a not so great hostel isn't the worst thing ever, so don't stress too much about it. Besides, you're going over New Year's so you probably will be out partying and not even there sleeping very much. Good luck!