Berlin hotels are very competitively priced by international standards. Adlon, Grand Hyatt, de Rome, Regent, Ritz Carlton and a few others are all at around EUR 200, or even much lower if you have a good corporate rate.

None sticks out in terms of particularly great (or bad) service, so in the end it comes down to style and location preference.

If you want to be at Potsdamer Platz (not a particularly nice area I find, because everything has been newly constructed after the fall of the wall and it feels a bit artificial - but very close to Philharmonie and convenient to many sights), then I would recommend the Hyatt. The Hyatt is contemporary, as you would expect, the Ritz Carlton is also as you would expect - columns, gold, dark wood etc.

If you want to be in Mitte, I would recommend de Rome. Very close to Gendarmenmarkt, in a refurbished old bank building (pool is in the former vault), esp. the first floor rooms with high ceilings have character.

I agree Adlon is great for a first time stay. It's in THE location 50 meters from Brandenburg Gate, but that also means many tourists crowding the lobby to have a coffee to be able to say they have been there (if you are unlucky).

The Hilton is very nice for a Hilton. Opened quite recently, and the location at Gendarmenmarkt is great, but given that it's about the same rate as the other, more luxurious options, I wouldn't know why to go there.