I have stayed at Hotel Rose Garden Shinjuku for 2 nights and I found this hotel has friendly service and it's conveniently located 1 min walk from Nishi Shinjuku Station (and about 7 min walk from JR Shinjuku Staton). There are also some convenience stores and McDonalds outside the hotel if you want to eat something in the middle of the night.

The room was very clean and it is also good sized for Tokyo. The bathroom was also very nice. Overall, I really enjoyed my stay at this hotel. When I go back to Tokyo one day (hopefully very soon), without doubt, I will stay at this hotel again.

We stayed in two hotels in Tokyo-Shinjuku during our stay: this one and the Best Western Astina. This was by far the best. Friendly staff, comfortable room, everything spotless, good value for money, good location at around ten minutes walk from the huge Shinjuku station (allow around 45 minutes the first time, as you will inevitably get very lost, both inside and outside the station - arm yourself with patience and just try to enjoy the experience!). Like other hotels in Japan, they provide slippers and pyjamas, which makes for a good photo opportunity.  Really would recommend this hotel.

An Ideal hotel for a single person on business. Its rooms are clean and quiet and staff friendly. Breakfast and dinner at the restaurant are tasty and priced reasonably. It is conveniently located on a main street with all kinds of restaurants, next to a subway station and only a few minutes walk from the Shinjuku station. It is my favourite hotel whenever visiting Tokyo without the family.

My wife and I stayed here from 4/28/11 to 5/2/11 on the last leg of a 2 week trip in Japan. The best thing about this hotel is it's proximity to the JR Shinjuku station. It's a 10 minute walk from the hotel through a safe and quiet area of Shinjuku. From the JR Shinjuku station you can get to any of the stops on the Yamanote Line in less than 15 minutes. There's also direct access to the Chuo Line which cuts through the middle of the Yamanote loop and travels further west to Mitaka (where the Ghibli Museum is). The JR lines make it easy to get to and from Narita and Haneda airports.
The room was expectedly small, but if you're only using the room as a place to sleep at night while you're out the rest of the day, it's perfect. We found the hotel to be clean and affordable (avg. $99 a night incl. taxes/fees), and close to several convenience stores, shopping centers, cafes and eateries. Access to the internet is available in-room with a 500 yen deposit for a LAN cable, which you get back when you return the cable at the end of your stay. We didn't eat at the hotel restaurant (a little on the expensive side) and opted for the several food options near the hotel instead.
Travel Tip: (This isn't about the hotel, but I wish I knew this before we arrived in Shinjuku) When you first arrive at the JR Shinjuku Station there are a few options to get to the hotel. You can either find the Marunouchi Line to take you to Nishi-Shinjuku Station, which is very close to the hotel but is owned by Tokyo Metro so if you are using a JR Pass it's not free. You can walk to the hotel but there are a few stairwells you need to take to get out of the station and a few elevated walkways (with more stairs) to get to the hotel, so if you have a lot of luggage it's not a fun journey. Lastly you can go to the taxi area right outside the terminal and take a cab to the hotel for about $10. The cab ride is very short, you don't have to carry your bags around and you don't have to tip. We suggest taking a cab when checking in and checking out, especially if you have a lot of stuff (we had 1 large rolling suitcase, 1 medium rolling suitcase, 2 duffel bags, and 2 backpacks).
We would recommend this hotel to travelers without children.