We stayed at the Adina Hauptbahnhof for 6 nights in December and were very happy with our choice.
The Adina is located an easy 10min walk to Hauptbahnhof station (main train station) which is the hub of public transport and hop on hop off tours in Berlin.
There are buses located everywhere around the hotel and everything is within easy walking distance.
We had originally booked a studio room but upgraded for €30 per night to the 1 bedroom apartment for the convenience of a working kitchen and washing machine / dryer.
There is a Lidl supermarket 5min walk from the Adina (past the hospital) which is really cheap for all sorts of food (compared to Australia)
If you like to shop but don't like to carry everything home with you in your suitcase there is a post office about 10 minutes walk in the opposite direction of Hauptbahnhof, so you can shop to your hearts content and send everything home cheaply!
Downstairs in the alto bar they have happy hour between 5pm - 7pm on most cocktails, beers, wine etc.
They don't advertise this always in the bar so be sure to ask about happy hour before ordering drinks.
The bar is a great place to sit and relax after a day of sightseeing and we always got a table whenever we went.
We dined a few times in the restaurant, very nice food and lovely ambience. The curry wurst on the menu quickly became a favourite.
Our room overlooked the inner courtyard and was quiet, with good heating and blackout curtains.
The rooms are large and bright, with very big bathrooms and the beds are very comfy.
Everything in the rooms are clean and modern, which was great.
There was a television in the lounge room and the bedroom - you cannot plug your laptop into these televisions.
The only real downside is that you still have to pay for Internet in your room, however as far as German hotel charges go, the Adina is quite reasonable charging for 24hrs usage, not time frame.
Thoroughly enjoyed our stay here.