We had a great time in Carmen's studio apartment. Cosy, well equipped and well connected into Central Berlin, it had everything we needed. Carmen was really helpful too: good communication, advice on getting from the airport and around, bikes to rent, offers of a warm fire in the evening.
The trains do run quite close to the apartment, so if you're a really light sleeper this might not be for you. It's a 20 minute walk from Friedrichshain's main eating/drinking area, which suited us well but does involve a bit of an extra walk.
And don't be put off by the arrival through an old bit of industrial East Berlin - all car workshops and warehouses - once you're at Carmen's place it's an oasis of plants, hammocks and log fires.