Great place for any budget traveller
I'm a little bit older than the standard backpacker ('30s) but I loved Wombat's. It is definitely a party hostel for those who want it, but since the bar and the common area are both far from the dorms and private rooms, those who want a little peace and quiet can get that as well. I even saw some families with young children--clearly this place works for most everyone!
On a map it looks far from the city center but don't let that bother you. It's so close to Westbahnhof subway and train stations that you can get anywhere in a snap.
Rooms are super clean and pleasant, and while the breakfast isn't free, it's the best meal deal you will find ANYWHERE in Vienna.
The only negative: there was a small glitch in our reservation (confusion over one double bed or two twin beds) so I would recommend you be very clear when making your reservation.