I'm a big history buff and we're going to be in the Alsace this summer. My non-history loving wife is allowing me to see one fortification - either Fort De Mutzig/Feste Kaiser Wilhelm OR the Schoenenbourg Maginot Line fort. Has anyone in this group been to either or both and can offer a suggestion as to which is more interesting? We'll have a car so transport isn't an issue.

I've only been to Fort De Mutzig and is way earlier than WW1, more like 1895. Underwhelmed but I have no comparison to really advise.

Different fortifications. Fort de Mutzig was built by Germany after the Franco-Prussian War and reinforced in WWI, handed over to the French in 1918, repaired/reinforced by France in advance of WWII, evacuated in 1940. Schoenenbourg was built by France in the 1930s and surrendered to Germany in 1940. I don't think either fortress saw significant battle action.

If your interest is primarily WWI, Mutzig is relevant and Schoenenbourg less so. Mutzig was "cutting edge" for its time. Concrete, electricity, radio links, ventilation. Probably more interesting overall if you learn its history and/or take a guided tour.