The Excelsior Hotel Ernst is the place to stay. They seemed to have had a recent renovation and the rooms are well appointed, nicely decorated and ample. The hotel lobby is a little dated, but the Hanse Stube is great and the bar is quite lively. The location is good for everything in Cologne as it's a tiny city and in this instance being so close to the train station isn't bad at all.
You probably couldn’t stay any closer to Cologne Cathedral without taking up residency within the gothic church itself. Along with providing a photo-worthy bedroom view, the upscale hotel’s location means it’s ideally positioned for the tourist trail (close to the Rhine, the Kölsch Beer Experience, the Museum Ludwig) and three minutes from the station, handy for transport. You don’t even have to leave the building for some of the city’s best food. The hotel hosts Michelin-starred restaurant Taku.