I stayed at the Hotel Xi for 5 days of meetings and a conference. The hotel has everything you need for a pleasant stay in a Mexico City hotel: a good breakfast buffet with custom made omelettes, terrific service from the staff at all levels, reliable and free wi-fi, comfortable rooms, an adequate exercise room (no pool), quiet at night so you can sleep well, a taxi sitio, and everything kept immaculately clean. The hotel is the former Quality Inn and has had a recent makeover with tastefully-remodeled rooms and bathrooms with ultra modern fixtures, and a few really ugly paintings in the lobby.
If you would rather get away from the busy traffic of Reforma and the high-end boutique atmosphere of the Polanco hotel strip, this hotel is centrally located and in a very nice area. The hotel is in Roma Norte, on a boulevard with a tree-lined promenade down the middle of the street. The street is lined with typical urban neighborhood businesses (pharmacy, hardware store, etc) as well as very hip coffee shops and restaurants which are beginning to creep in from the adjoining Condesa restaurant district. If you want to be in the center of Mexico City's hipster scene (think Park Slope in Brooklyn), you can walk into the heart of Condesa in about 15 minutes.
Only a few negative comments: Be careful of the killer marble and tile floors - in your bathroom and in the lobby, be VERY careful of how slippery the floors are when wet - and remember that Mexico has no "slip-and-fall" personal injury liability law. The management might think about upgrading the bedding, towels, and toiletries.
Hotel Xi is perfect for folks who like Mexico City's lovely neighborhoods. I will definitely come back!