Mercure is in Friedrichshain but on the border of Mitte and Kreuzberg. Uptalsboom is in the heart of Friedrichshain. Hotel Johann is in Kreuzberg again. Kiez Pension appears to be a boarding house, however in the heart of Friedrichshain. None of these locations is in the heart of the action but in tram/subway distance. I would - seriously - do it the other way round: Chose a hotel in the heart of the city and take the subway/tram to Friedrichshain. Distance is about 20 minutes, however being in the heart of town might be nicer.