Forget about the Melia. Sorry, but this is not a location where one has to be.

In your shoes, I (as a born Berliner) would chose the

Hilton, Dorint, Hotel de Rome or the Regent,all directly on Gendarmenmarkt (Hilton is my favorite with Gendarmenmarktview)

Westin, directly at the crossroad of Friedrichstraße and Unter den Linden or

Adlon, directly at Brandenburg Gate.