My boyfriend and I stayed at Hotel Mistral in April at the start of our five week backpacking trip through Europe. The hotel was easy to find from Gare de Montparnasse and upon arrival although our room wasn't quite ready because we were early they were more than happy to store our bags and get the room ready within half an hour.
The location has great access to the catacombs and the train station that takes you to Versailles (if visiting Paris do not miss a trip out to the chateau). There are some great restaurants just around the corner which are lively and fun and not as busy or expensive as the restaurantes in the touristy areas. A great way to experience the Parisian culture.
Notre Dame and the Louvre are walkable (we walked everywhere and it was never an issue) but for quick access the metro is also close to get to all of the main sites. It is also very easy to get to the main train station if you are travelling on from Paris to another city.
The hotel has complimentary wifi, a warm and cozy lobby and an eating nook that is quiet and comfortable. They also have a great quart yard area just outside the eating nook.
The room is small and simple but serves all the purposes of a backpacker and since we basically just needed a place to sleep it was perfect. We were even upgraded to a room with a private bathroom instead of the one we had booked with a shared bathroom. There is no lift just stairs but it didn't bother us in the least. The hotel is well marked from the street and we would definitely recommend staying here. The price is great in comparison to what is offered at other hotels and because there is so much to see and do in Paris it is good for a short or longer stay.