It's four nights so you really have to decide where you would like to go. Sometimes we drive ourselves crazy looking for the best "yield." I wrote earlier that I went on a magnificent cruise from Venice to Athens, we flew First Class on Swiss and since I had some free nights, decided to stay in Zurich on the way home.
This was totally driven by trying to make the most of some free nights and guess what? We had NO desire to stay extra nights anywhere but just wanted to get home. Weather sucked and yes, the hotel was wonderful but sometimes you need to think of the other considerations. Travelling to Europe for 4 nights could be crazy!
In this country, we LOVE the PH Washington DC and the Andaz 5th Avenue in NYC has great reviews. Think of what area would work for you, so a search of this forum for hotels in this area and go from there! Enjoy.