Which district to stay at in Tokyo?

My dad and I are going to spend a week in Tokyo in January, and I was just wondering what would be a nice district to book our hotel in? My main concern is that I want it to be a family-friendly and safe environment (in other words, no raging nightlife around the hotel) and one with nice comfortable hotels (price is not an issue, so if it's expensive, that's fine).

Also one other question: we will mainly be travelling inside Tokyo, exploring the different districts, but we might also do a day trip to Yokohama or a neighboring city. For this situation, which train pass is best? Or is it best not to buy a pass at all, but buy each train ticket as we go along?

Thanks for your help!!

According to your desire, I would recommend you 'The Peninsula Tokyo', one of the newest and grandest hotels in Tokyo, very close to Ginza, Yurakucho and Hibiya stations.
If you are just visiting Yokohama, you don't need the JR pass, because you can take the JR Tokaido from JR Tokyo station to JR Yokohama station which costs you just 480 yen. Or you can take the Toyoko line from Shibuya to Yokohama and other interesting spots.

I have stayed at the Sawanoya Ryokan 3 times. It is located in the Shitamachi district (old downtown) near Ueno station. It is a traditional type of lodging with mattress and futon on the floor. The neighborhood is very safe and easy to walk in and just a few blocks from Nezu station on the Chiyoda Subway line. There are lots of restaurants and stores around but it's mostly residential. It's modestly priced and clean and comfortable. They serve a very inexpensive breakfast and the staff is delightful. Here is their website:
http://www.tctv.ne.jp/sawanoya/
Nezu shrine is located nearby as well as Yanaka, a hilly neighborhood of homes, temples and shrines.

Since the rates doesnt matter, I recommend Azabu area in Minato district, Tokyo.

It's the most internationalized area in Tokyo, where ambassy officers from Europe and America live. Everything is offered under western manner. Apart from the rates, it should be the most confortable area for foreigners in Tokyo.

The Mandarin Oriental is also in a safe district, a 5 minute taxi ride from Tokyo Station:
http://www.mandarinoriental.com/tokyo/

And the Park Hyatt, Regency Hyatt, Hilton Tokyo and Keio Plaza are all in Western Shinjuku, which is a nice, interesting, convenient and safe area.

Thank you all for your input! I will look up all the hotels and areas you suggested.

I read some reviews on tripadvisor.com, and it seems like the Royal Park Hotel (I think it is in Nihonbashi or near it) is loved and recommended by everyone who has stayed in it (it even recieved the #1 rank for hotel in Tokyo on that site). It says the hotel is in "shitamachi" (I'm assuming this means its a nice, quiet neighborhood?). Do you guys think this hotel would be a good choice? Or would it be too far from central tokyo?

Please let me know your thoughts.

the Royal Park Hotel is right downtown, with easy access to/ from Narita airport. Check their own site:
www.rph.co.jp/english/

click on the tab "rooms" for photos and rates. it is pricey ($ 400 average per night for a twin) but looks great. there are other hotels with similar names, like Park Hotel etc. one of them located in the Shiodome complex, another great location. I once stayed in the Hilton in west Shinjuku and due to a mistake in booking we were upgraded to a suite with several rooms in Japanese style plus a huge western style living room and it was more than great. AT THE TIME (2002)it was US$ 1000 per night (they charged us much much less less) so if you really want a memorable room no matter the cost have a look at suites in the Park Royal and other hotels.
It appears that you aren't quite familiar yet with Tokyo downtown. please try to find a map on the internet, including a map of the Yamanote Loop line and/or get a guidebook. Most hotels internet sites have access maps but you need a downtown Tokyo map to get a better idea of where they are.

shitamachi means more or less the old Tokyo Asakusa, Ueno, Ginza etc.)as opposed to say West Shinjuku that is a newer (relatively)area.
check
www.japan-guide.com/e/e3004.html
for information and basic maps on Tokyo

Not really related to the question, but Ginza has always been too upmarket and too close to the Imperial Palace to be considered part of shitamachi- Ueno, Asakusa and other districts in the northeast of central Tokyo are shitamachi- areas like Yanaya, Nippori etc are all shitamachi as well- more working class areas than Ginza. Shitamachi was a particular part of old Tokyo.

, though everything was burned down during Great Kanto Earthquake and WW2 and is a reconstruction at present.

I included Ginza because I was thinking about shitamachi in the olden days. Tsukiji, for example, is the type of business that was found in the working class parts of many cities around the world (like Covent Garden in London and Les Halles in Paris. They were both once wholesale food markets and are now touristy areas with "chichi" boutiques as the French say)

I see, for some reason I thought it was in Northern Tokyo xD

Thank you for all your help!!