I would say this definitely depends on what you want in an experience and what you like in a kolsch.
Reissdorf was both the best beer to me and the best vibe as a place. The beer was extremely balanced and flavorful. Malt forward and bready with a firm bitterness to even it out. A little fruity but mostly clean to me. I never got tired of drinking it. They have a restaurant that's a bit outside of altstadt and is much more cozy and low profile than the big beer halls. It was more of a neighborhood joint. Still
very gorgeous and elegant inside.
Paffgen was also relatively low key at least when it wasn't peak hours. They are also a little ways away from the dom, closer to Reissdorf, and so also not nearly as touristy. People were there just reading books or hanging out. I'm sure it amps up during really high volume times. It's also definitely a little more old school and grungy. Not gross or anything but more beer hall leaning than Reissdorf. The beer was less rich and flavorful to me than Reissdorf but it was very light, well-balanced, and easy to drink. Maybe a little sweeter with more hop character pushing through. I could sit there and drink a few, for sure.
Peters is still off the dom some but in a different direction. It's more of a beer hall for sure. Very pretty and was still relatively relaxed with families eating dinner and enjoying their drinks. A little busier and would probably be very bustling during peak hours. The beer was thinner and more hop and ester forward. That's in comparison to the others above, though. It wasn't thin by any means and hop and yeast character was still restrained. Very crisp and very drinkable. Similar to Paffgen above I would definitely go back again.
Fruh has a very pretty beer hall right on the dom. It felt the most touristy to me, though, and I honestly didn't love the beer. That might just be my taste, though. It was more minerally and salty and was light but didn't feel as crisp. It was pretty bitter in a way that didn't feel cohesive with the rest of the beer to me too. Having said that, I still got a second one and I enjoyed it. The beer was good and well executed. It was just not my favorite and the place was not my particular vibe. If you're looking for a nice, big beer hall where you can step outside and see the dom then this is a good candidate, though.
Gaffel also has a beautiful beer hall. I can't speak to the beer on tap there because we went even during relatively off hours and it was still totally packed. We walked through and couldn't even find a spot at all. We left with the idea of going back but it just didn't happen. If you can find a time, maybe lunch, where you can find a seat then I bet it's worth a visit. The place was big and very pretty. My experience with Gaffel at other places around Cologne, and in bottles around Chicago, it's smooth, crisp, and very drinkable with a little more hop character and pretty noticeable esters. Tasty, but not necessarily special or something I would personally say you specifically need to seek out as a top-tier kolsch. If you want a pretty beer hall and a tasty beer then Gaffel am Dom is a good candidate. You walk out the front door and it's just...cathedral!
Bonnsch is just a bonus if you happen to be going to Bonn on the trip. It's a beautiful space and the food is very, very well done too. The beer is more unique with its own Bonn twist. Their Bonnsch/Kolsch is very lemony almost to the point of feeling like a shandy. It was also very creamy and a little cloudy with a noticeable yeast profile that played well with the lemon and made for a very interesting beer. It would be a beautiful beer to drink during the summer. They are also less bound by tradition so they will have at least a couple other beer styles on tap. I had a pretty tasty pils and I think a pale ale as well while I was there. They brew a variety of other styles too including an alt
Definitely a jewel of Bonn. If you need an excuse to get your wife to Bonn then the botanic garden is also really beautiful. They even have a couple Giant Sequoias. They also have a blossom street that is probably still very pretty in the summer (Kirschblute), a Japanese garden, and some very pretty hikes just south in Konigswinter.
If you have questions or are going anywhere else nearby just let me know. My one plug would be for Koblenz, though it's a bit far. It is absolutely amazing and would be a wonderful summer day trip or longer. Nice little mid-sized city with gorgeous views and a rich, interesting history. A beautiful old cemetery, super interesting fort, and some wonderful hikes with amazing castle views. The altstadt is not too crazy and the eck is pretty and has a lift that can take you up to the ehrenbreitstein fort.
