Koln, Koblenz, Trier

When I was in Köln (please note the spelling), I stayed at the CityClass Europa am Dom hotel. It was right next to the cathedral (in fact, I had a view of the cathedral from my window), and was very nice and quite reasonably priced. I booked it at the last minute because my first hotel choice had fallen through, but I really enjoyed my stay here. It was very convenient to the sights and shopping, along with some very pleasant restaurants nearby, the staff was pleasant and the room very clean and spacious.

We stayed at Hotel Trierer Hof in Koblenz some years ago and see that it's still seeing very good reviews. Room was very clean; bed comfortable; really good location; good breakfast; price was right. Not fancy but more than fine for what we needed. No air conditioning but we didn't need it.

https://triererhof.de/en/
https://www.booking.com/hotel/de/trierer-hof.html#tab-main
https://www.tripadvisor.com/Hotel_Review-g187391-d632940-Reviews-Trierer_Hof-Koblenz_Rhineland_Palatinate.html

When I'm in the area, we stay down at Bacharach--just south of Koblenz. It's a very popular city on the Rhine River. And some trains stop there on the way to the Frankfurt Airport.

All accommodations in Bacharach are perfectly good. We last stayed with a lady that owned the local bakery, and her breakfasts were just great. Rick Steves took a liking to this city and personally put it on the map for travelers.

We also like to stop at Koblenz at the Koningsbacher brewery for an afternoon of sitting in their beer garden watching the cruise ships go up and down The Rhine.

You'll get more suggestions if you post this is the GERMANY section. You have it posted in the GERMANY REVIEWS section which is a place for YOU to GIVE US a review of somewhere you've been. Also, you can do a SEARCH in the search bar above as I'm sure others have asked this question.

We've stayed at the Hilton in Cologne twice. It's shiny modern and more expensive, but very comfortable, and a huge breakfast buffet. Probably additional cost, but I don't remember. Keep in mind that Cologne is famous for being 80% walkable from the HBF, so do not take a bargain hotel that requires a subway ride to start your sightseeing. (the Ethnographic, Medieval Art, and Kathe Kollwitz museums require public transit from the main area.)

It was ten years ago, but we were unable to find up to date housing in Koblenz, so we stayed a few towns away, but I don't "recommend" that. However, Koblenz has two train stations, which makes a commute convenient.

As others hinted, you did not ask about the "scenic Middle Rhine" boat ride, typically Bingen to Boppard or nearby. No other area needs to be boated, including Koblenz or Cologne. Please give time of year and budget if you post again.