Which of these Alsace wine region towns should I visit in one day?

We stayed in Ribeauvillé and it has one of the larger medieval centers and 3 ruined castles above the town. It also has the largest wine cooperative in the region, dating back to 1895. You can tour medieval Ribeauville and then taste a Riesling or two while waiting for your return bus which will stop
near the cooperative. Riquewihr is amazing and unique because of its castle, medieval gateways and fortifications. It also was home to the person who, centuries ago, was responsible for the term “Gourmet.”

Pope Leo IX was born in Eguisheim when it was actually part of Germany. The church and town are crazy adorable. We stayed in the town at a working winery. https://frenchmoments.eu/eguisheim/ Tasting is available whether you stay with them or not.

https://www.tourisme-eguisheim-rouffach.com/EN/Domaine-GINGLINGER-Paul-f253001030.html

It's a difficult choice to make. Since you only have time for 2 villages, I would eliminate Hunawihr. I don't think there's enough to keep you occupied until the next bus.

Ribeauville, Kenko has given you a summary. It is the largest of the villages.

Riquewihr, as Kenko pointed out, has medieval gates and fortifications, with its winding streets giving it a fairytale feel.

Kaysersberg, lovely village on a river, the birthplace of Albert Schweitzer

Eguisheim is smaller than those above, Jules' description of crazy adorable is perfect.

Turckheim is the least touristy of the 5 villages with a nice little WWII museum on the Colmar Pocket.

All the villages have their own charms and feel and deserve some time.

Before catching your train back to Strasbourg, visit the Little Venice area in Colmar's old town.

Last year in early June, we used the Kutzig bus and stopped at Riquewihr and Kaysersberg. Riquewihr was mobbed so we left as soon as we could, so keep in mind it might be very crowded. Perhaps others will comment on their recent experiences. If less crowded, I’m sure we would have liked it. The village of Kaysersberg was lovely. We could have visited a third village, but chose not to.

We found Riquewihr delightful (same for all the others), We were in Riquewihr by about 8:30am. Better for finding parking and the crowds (and I mean CROWDS) didn't show up until about 11. I'm guessing some of that was tours arriving.

Do you enjoy walking/hiking? If so, you might like to follow our itinerary. We took the bus from Colmar to Ribeauville, which is very picturesque. From there we hiked up to three ruined castles, which was a lot of fun. Then we walked through the vineyards to Riquewihr, another appealing village. From there, we bussed back to Colmar. It was a very enjoyable day. We were there in March, so there were no crowds at all. Sorry, I do not remember where we ate lunch.

Thanks for all the input! Sounds like Riquewhir might be best to head to first before it gets to crowded. We do enjoy hiking, so I'll look into that option!

This may be late as a timely reply but may still be informative.

My artist sister and I (am a man) visited Riquewihr and Hunawihr last July 2023 and we really love both. After touring some shops and the tower, we hiked up to the vineyards on the hills beside Riquewihr, took pictures and videos of the town below, got amazed of Riquewihr's beauty, then continued our way hiking to Hunawihr pausing along the way to admire the views, got amazed of how quiet the place is, appreciated the small butterflies which we encountered (my sister loves butterflies), picked some small fruits, until we reached Eglise mixte Saint-Jacques-le-Majeur de Hunawihr. Interestingly, we met only 3 people along the way to Hunawihr. We reached and entered the church from its side or back door and when inside it, we noticed some frescoes (I hope that's the correct term) and a diorama of the evolution of the fortified church. Outside the church, we visited the graves of the locals and observed how affectionate they are to their lost loved ones which moved me to tears. We then noticed on the bulletin board an information of the church being both Catholic and Protestant which surprised us since it was our first time to encounter such set up. After taking pictures and videos in front of the church and hearing its bell ringing, we proceeded to the streets and admired how old the houses are. After that, we dined at Chez Suzel and tasted local food. Oh it was already past 9:20pm and we had to hike back to Riquewihr. So, we hurriedly hiked back to Riquewihr with a bit of fear that we might get lost but also imagining for fun as if we were Hansel and Gretel though not in a forest. We finally reached that part of the road overlooking the town at around 10:07PM which was already twilight. Each of us took videos and pictures of the beautiful town below with selfies of course. The sight of the town at twilight and the ringing of the bell of Eglise Protestante Sainte-Marguerite are sooooo beautiful and thanks to Riquewihr's remote location from the big city and with its surrounding hills, it is not influenced or consumed by other surrounding lights. I vividly remember this very beautiful experience of Riquewihr and Hunawihr in our trip. Oh what an experience! We then scaled down the slope of the vineyard and got back at the main road Rue du General de Gaulle at around 10:30 PM and the town was already so quiet and void of tourists. I took some photos and videos then headed back to our hotel.