Been living here for 5 years. Always see loads of people on the forum talking about how much they love the city. It's certainly great to visit, but the novelty of living here quickly wears off.
I'd look for a place as far from Kreuzberg as possible. Full of hipster c**ts and some of the shared areas in the apartment buildings look like crack dens.
Generally, I find the city noisy, crowded and dirty but I suppose some people enjoy the 'grungy' atmosphere. Areas on the edge of the city are maybe an option if you prefer things a little quieter. I live near Spandau, and I'm surrounded by some nice lakes and green areas.
Give me a shout if you get further along in the process and I'll happily help you out.
I would do A LOT of research on the taxation and insurance systems as a priority. Depending on your job, they can be a nightmare and incredibly costly, and the bureaucracy here is the worst of any country I've lived in. Like I say, give me a shout if you need any help.