Best location to stay in Berlin?

Mitte is probably the best, and consequently the most expensive. I stayed at the Mercure Checkpoint Charlie and it was a great location. (BTW a friend of mine who lived in Mitte for 5 years is going back to Berlin for a few days and he's staying at "my" hotel.) Other friends staying near Alexanderplatz and were very satisfied with the location.

Mitte is as has nbeen said the best for a first time tourist.I made the mistake of staying in Stigelitz, fine enough area but too time consuming to get to and from the sites I wanted to see especially as then (2 years ago) there was major work and diversions on the S Bahn line I used.
Alexanderplatz is very popular and my favourite micro brew pub is near there,most of the folk I know have stayed at the huge Park hotel

Steglitz is a residential area. I went to it once...in 1999 to track down the house of a well known author in German lit.

Fred it was quite handy for me as I was staying at the Best western which was right beside both U Bahn and S bahn stops, easy to get out to the house of the Wansee confrence which was my main Must Do but the group I was with were not so enamoured of the place as they did not like all the travelling,but as i am very used to public transport in many cities I find it relatively easy.

@unclegus...The house in Steglitz was that of the author Kurt Tucholsky Your group did not want to stay in Wannsee since that site, the House of Wannsee, was your goal in the first place? Whenever I had to change trains or the S-Bahn at Berlin-Wannsee station, most often a good number of young folks were on the platform too.

We stayed at the Adina Hotel at Hackescher Market and found it to be an excellent hotel and location.

It's not really in one of Rick's "fun neighborhoods," but I highly recommend mittendrin, located just off the Ku'damm, about half-way between KaDeWe and Kaiser Wilhelm Memorial Church. A friend and I spent a week there last May; it was so enjoyable, we are returning for a week this May. The owner is Sabine, an actress from Munich who is one of the loveliest hosts you will ever encounter. She calls her place a "boutique hotel;" I call it the world's best B&B. Sabine is eager to help her guests enjoy Berlin and joins them at a large table in the common area each morning for a breakfast that is simply amazing. The place only has 4 rooms -- 2 share a bathroom and 2 have their own bathroom. Transportation is excellent -- there are 3 U stations within 2 blocks. It takes 15 minutes to get to the Brandenburg Gate (one transfer), 18 minutes to get to Alexanderplatz (no transfer). For my friend and I, staying at mittendrin seemed like sleeping at the home of a dear old friend. Perhaps that better matches your definition of "back door" than a chain hotel in the city center?

We found the Mitte convenient, fun and a good starting place for all our walking. We stayed at Hotel Adelante Berlin-Mitte and would go back in a heartbeat. It had the best shower I've had in Europe!