Strasbourg has more character. Xmas market is great. Colmar is pretty blah. As for restaurants you should PM Panos Kakaviatos as he is from Strasbourg. You really should hit one of smaller villages like Ribeauville or Riquewihr since you will be there.
I agree with Paul. I find that Colmar’s buzz exceeds its actual charm, at least relative to several other similar towns in the area.
I like both the Winstub and the starred restaurant at the Chambard in Kaysersberg, and I love that town—though it’s small and doesn’t offer the diversity of activities you will find in Strasburg or even Colmar.
Strasbourg is larger and more interesting (and with better food and lodging). Colmar is interesting for a morning or afternoon, either starting or ending with a visit to the Underlinden museum to see the Isenheim Altarpiece and a lunch of tarte flambee and Riesling. You can easily train there from Strasbourg, but I like driving around Alsace as it is more efficient than taking trains and it an easy region to navigate.
Unless you plan on not leaving Strasbourg, you really do need a car. And I didn’t think driving in Colmar was a problem, though if you’ve never driven in Europe, it is definitely different than driving anywhere in the US.
Put Eguisheim on your list of smaller towns to visit. And I’d second the recommendation for la Taverne Alsacienne, though a dinner in Ingersheim probably isn’t practical if you’re staying in Strasbourg.
I strongly preferred Colmar to Strasbourg from a scenic standpoint, it was small, not at all built-up. I can’t compare the two because we only ate at a cafe across from the the Strasbourg train station. If you only have a day, you wouldn’t be able to see all of Colmar, anyway, so you might as well choose the restaurants you like and then go there. We ate at the * Jy’s and it was good but not spectacular.
We bicycled through Alsace this past fall staying in both Strasbourg and Colmar as well as Riquewihr, Savenne and Obernai. Riquewihr is charming and worth a visit but not a lot to do except the tourist stuff and of course wine tasting. Strasbourg is very charming and the boat ride alone was worth the trip. Do rent the car and travel it will not be a hard drive