Just got back from a one-night stay at Hilton Cologne -- overall positive experience, easy access to main railway station and cathedral (2-minute walk) if you're touring instead of working, river, easy access to multiple restaurants (and breweries if you like). Desk and concierge friendly and helpful.
They put me into one of the larger rooms though I'd paid for a base room, modern styling, everything worked.
Room was not ready on arrival (it was only 1PM so I wasn't sure it would be) and they gave us complimentary drinks at the bar during the 20 minutes we waited even though we were early.
Welcoming plate with chocolate covered fruit and strawberries in room was a nice touch.
Breakfast buffet was abundant and tasty but as stated above crowded -- had to sit at the other end of a table already in use by someone as there was no room elsewhere, but that used to be routine in Germany even in restaurants so it was no big deal.
Would definitely go there again.